As a large province with forest resources, assessing the value of forest ecosystem services in Yunnan is of great significance to maintain the sustainable development of Yunnan's economy. Based on the latest survey data of Yunnan Province, i.e., the forest resources type II survey data, and in accordance with the Specification for Forest Ecosystem Service Function Assessment (GB/T 38582-2020), the value of forest ecosystem service function of 16 cities (prefectures) in Yunnan was assessed, and the ridge regression method was used to study the main factors affecting the value differences among cities (prefectures). The results show that: (1) The value of forest ecosystem services in Yunnan is 982.926×10⁹ yuan yr^–1, of which the value of carbon fixation and oxygen release is the largest. (2) The top four cities (prefectures) in terms of value of services are Pu'er City > Chuxiong Prefecture > Diqing Prefecture > Dali Prefecture; the bottom four cities (prefectures) are Kunming City > Yuxi City > Dehong Prefecture > Zhaotong City; (3) The main factors affecting the value of the service function of each city (prefecture) are forested land area, forest cover, GDP and population density. The findings of this study provided a reference for the sustainable development of the ecological environment in the prefectures and cities of Yunnan Province.