As an ecological asset, ecosystem is closely related to human welfare. It is of great significance to evaluate the value of ecological assets and quantitatively distinguish the relative contribution of human activities to the change of ecological assets for assessing the effectiveness of regional ecological civilization construction, ecological compensation, and natural asset audit of cadres leaving office. Based on the method of equivalent value factor per unit ecosystem area, this study redefined the standard ecological assets value equivalent factor, and constructed a method that could quantitatively distinguish the relative contribution of climate change and land use change to the value change of ecological assets. Taking Fangshan District of Beijing as an example, this study analyzed the change of ecological assets in Fangshan District from 2000 to 2019, and the relative contribution of climate change and land use change to the change of ecological assets. The results showed that: (1) the total value of ecological assets in Fangshan District in 2019 was 17.714 billion CNY. The value of ecological assets of forest, grassland, farmland and wetland respectively accounted for 82.33%, 11.76%, 5.25% and 0.095% of the total value of ecological assets, respectively. (2) From 2000 to 2019, the total value of ecological assets in Fangshan District increased by 2.275 billion CNY. Climate change increased the total value of ecological assets by 2.689 billion CNY, while land use change reduced the total value of ecological assets by 0.414 billion CNY. (3) The value of ecological assets in Fangshan District was high in the west and low in the east, of which the total value of ecological assets in Xiayunling Township was the highest. The ecological assets in Liulihe Township increased the most, while Gongchen Street decreased the most significantly. The past 20 years have been a period of rapid social and economic development in Fangshan District. Due to climate change and ecological protection and restoration, the value of ecological assets has increased, offsetting the loss of ecological assets value caused by the expansion of construction land.