Ecosystem assets are important natural resource assets and the basis of high-quality ecological products provisioning. The change trend of ecosystem assets can be used as an important indicator to measure the effectiveness of ecological protection and restoration. Shannan City has various types of ecosystem assets on the Qinghai-Tibet Plateau. Taking Shannan City as an example to carry out ecosystem assets accounting can provide reference for the evaluation and protection of ecosystem assets in the Qinghai-Tibet Plateau. Based on the area and quality of ecosystem assets and the ecosystem assets index as the main indicators, this study reveals the changing trend and influencing factors of ecosystem assets in Shannan City from 2000 to 2015. The results show that: 1) In 2015, grassland and forest were main ecological assets of Shannan City, accounting for 40.6% and 35.8% of the total ecosystem assets, respectively. The quality of ecosystem assets in Shannan City is low, and the proportions of excellent and good grades are 11.8% and 12.0%, respectively. The index of ecosystem assets in Shannan City is 38.26, and the indexes of grassland, forest, shrub, and wetland are 16.23, 14.88, 5.27, and 1.78, respectively. 2) During 2000 to 2015, the area of ecosystem assets in Shannan City had little change. Forests and desert ecosystem assets increased by 50.2 km² and 43.9 km², respectively, while the area of wetlands, farmland, grassland, shrubs, and glaciers decreased by 97.4 km², 29.8 km², 2.9 km², 2.7 km² and 0.3 km², respectively. The quality of ecosystem assets was significantly improved, with the growth rates of excellent and good grade ecosystem assets being 40.5% and 108.5%, respectively. The ecosystem assets index of Shannan City increased by 16.1%. 3) The changes of ecosystem assets in Shannan City are mainly affected by such factors as sloping land conversion program and other ecological protection and restoration policies, urban expansion and climate change.