Geographical environment Ya'an City is located on the western edge of the Sichuan Basin and is located in the peninsula mountainous area in the transitional zone from the Chengdu Plain to the Qinghai-Tibet Plateau. It was known as the "Tsing Yi Kingdom" and was the capital of the original Xikang Province. The geographic location is 101 degrees to 103 degrees east longitude, 28 degrees to 30 degrees north latitude, 515.97 to 5,793 meters above sea level, and an area of ​​1,205,600 square kilometers. Under the jurisdiction of Yucheng, Mingshan, Tianquan, Lushan, Baoxing, Sutra, Hanyuan, and Shimian, there are seven counties and one district with a total population of 1.54 million. Affected by the continental monsoon climate and warm southeastern humid air in the mainland, the city is surrounded by mud and mountains. The precipitation in one district and five counties in the northern part is rich, with an annual average of 1500 mm or more. There are fewer sunshine hours, and the annual sunshine hours are only 800 to 1050 hours; the air humidity is high. Relative humidity is 80 to 83%. There is the title of "Xishi missed sky" and "rainy city." In the mountains, the soil contains sandy soil or gravel clay with more organic matter. The top soil layer is deep, the structure is soft, nutrients are abundant, drainage is easy, and it is suitable for the growth of tea trees. Ya'an has four distinct seasons, no summer heat, no cold winters, rainy, cloudy, foggy and unique geographical conditions. As early as the Western Han Dynasty (53 BC), local people Wu Lizhen planted tea in Mengshan, which was recorded by humans. The earliest place for planting tea was the birthplace of the world's tea civilization and the birthplace of tea culture. Mengshan tea from the Tang to the Qing emperor royal family, "Yangtze River water, Mengshan top tea" well-known. In December 2001, Mengshan Tea's geographical product protection was approved by the state and became the second country in China to protect products originating from tea. Ya'an is rich in natural resources, with unique natural conditions, excellent and rich varieties of resources, a sound tea seed breeding system, and tea garden construction throughout the city's districts and counties. Unique ecological environment for optimum tea growth: The average annual solar radiation is 350.90KJ/CM, which is the highest in August, the least in February, a difference of 2.8 times, and the average annual sunshine hours is 989.7 hours, accounting for 24% of the hours; the interannual variation is large. The maximum number of years is 2.2 times the minimum. The month-to-month change was the highest in August, at 114.4 hours, and the lowest in February, which was 49.2 hours. The average annual temperature was 15.4°C, the highest year was 16.1°C, and the lowest was 14.7°C, with a variation of 1.4°C. January was the coldest, with an average temperature of 5.4°C; July was the hottest, with an average temperature of 24.4°C; and a year-on-year difference of 19.0°C. The extreme maximum temperature is 34.7°C and the extreme minimum temperature is -5.4°C. The difference in the number of days of the four seasons is 8 to 19 days. The number of days in each season is greater than 80 days, of which the winter is 100 days longer, and the fall is 81 days. There are distinct four seasons of climate characteristics, but the winter has no severe summer and no summer heat. It is in line with the annual accumulated temperature of 4790.3°C when tea plants begin to germinate at 10°C, which provides a good environment for the growth of tea plants. The annual growth period reaches 9 months. The annual average rainfall is 1501.5mm, and the most years are 2118.7mm in 1964. The minimum years are 1987. At only 1040.1mm, the most years are more than twice the minimum at least. During the summer and autumn from May to October, the average precipitation is 1297.1mm, accounting for 85% of the whole year, and the average of only 222.8mm in the winter and spring from November to April, accounting for 15 of the whole year. %. Summer accounted for 58% of the whole year, winter accounted for only 4%, summer was 16.5 times that of winter, and monthly changes were the highest in July, being 371.9mm, followed by August, the lowest in January, only 18.1mm, the highest month was 21 times the minimum month. The change of day and night, the nighttime rainfall is more than 2 times of the daytime, the average annual rainy date is up to 200 days, which is conducive to the growth of tea trees; the average annual evaporation is 94.9.5mm, accounting for 67% of the annual precipitation; the average annual relative humidity is 82%, It is one of the domestic high humidity areas. The rainfall is abundant, there are many rainy days, and the average annual rainfall is 277.2 days. There is less sunshine and more air contains water. It is closely related to the production of famous tea. There is more light fog, less dense fog, the annual average density of fog is 9.4 days, and winter accounts for 48%. It accounted for 30%, the least in spring and summer, accounting for 11%; the depth of farmland was deep, and the soil with thickness over 80cm accounted for 88.4% of the farmland. The soil texture is heavy, with heavy and light loam accounting for 81% of the cultivated land, medium soil 13.3%, light and sandy soils, etc., with only 5.64% of the soil. The soil pH is mostly acidic due to the influence of the parent material and climate. It is slightly acidic, accounting for 74.19% with a PH value of less than 6.5; 90.8% with an average soil organic matter content of between 2% and 4%; 88.9% with an average total nitrogen content of 0.1% - 0.2%; and an average available phosphorus content of 10 - The percentage of 40 PPM is 99.7%, and the average content of available potassium is 88.5% at 100-200 PPM. In general, natural conditions are characterized by a deep soil layer, acidic reactions, no cold winters, no summer heat, and unique natural conditions that are ideal for developing the tea industry. The natural ecological conditions and superb teamaking skills of the superior Yicha tea have created the good quality of Yaan Tibetan tea.