The ecosystem accounting can offer quantitative evidence for evidence-based decision making in ecological civilization building, including ecological asset accounting and ecosystem services accounting. However, the ecological asset accounting system has not reached a consensus by stakeholders. Ecological asset indicates the ecosystems that provide ecological goods and services. In our study, we took the north district of Tanggula Mountain (Tangbei District for short) as a case to do a comprehensive ecological asset accounting. The biophysical account and changes sheet, profit and loss account sheet were built. We established a composite index of ecological asset. The results revealed that the grassland ecosystems were mainly of good level (68.46%). The wetland ecosystems were mainly of excellent level (59.72%). There were 138 kinds of wild fauna and flora, of which ten were state-level key protected animals. The composite index of ecological asset was 79.77 in 2015 that decreased by 3.60% from 2000 to 2015. During the fifteen years, the ecological assets of wetland ecosystem and grassland ecosystem increased by 164.23 km² and 2.82 km², respectively. The wetland asset increased by 202.90 km² mainly because of wetlands recovery (200.50 km²) and decreased by 38.63 km² mainly due to wetland degradation (36.23 km²). The grassland ecosystem asset increased by 39.18 km² that mainly caused by grassland expansion and decreased by 36.26 km² that mainly caused by wetlands recovery (26.20 km²) and desertification (9.65 km²). The comprehensively accounting system of ecological asset meant a lot to implement outgoing accountability regime so as to build ecological civilization in China.