Forest ecosystem is main habitat of Yunnan snub-nosed monkey (Rhinopithecus bieti) (YSM). The change of forest area is considered to be a direct impact to YSM existence. Based on Global Forest Change data, using Theil-Sen trend analysis, Mann-Kendall test, hotspot analysis and geographical detector model, this research discussed the spatio-temporal characteristics and determinants of forest area change in the distribution area of YSM from 2001 to 2019. The results showed that: (1) During the past 20 years, the total forest area change in the distribution area of YSM was 3.81×10⁴ hm², about 2.44% of the total forest area in the study area, annual forest area change showed a large inter-annual fluctuation, in which 5456 hm² forest area change in 5 protected areas, accounting for 14.3% of the total forest area change in the study area. Forest area change ratio was relatively higher in Laojunshan scenic spot and Yunling nature reserve. (2) Forest area change trended to mitigate in the distribution area of YSM. The significantly increasing area of forest loss was 1.03×10⁵ hm², accounting for 2.9% of the whole study area. The significantly decreasing area of forest loss was 3.05×10⁵ hm², accounting for 7.9% of the whole study area. At the same time, the hotspot areas of forest area change showed a decreasing trend. (3) Forest area change showed a trend of shifting to low altitude and high slope area in the distribution area of YSM. (4) The burned area and population density were main impact factors of forest area change in the distribution area of YSM, followed by precipitation, altitude and temperature. This study has practical significance for forest ecosystem management and YSM conservation.