Abstract: Evaporation is the key item of water balance calculation. Clarifying its characteristics will be helpful in water resources assessment. The Golmud river catchment is a typical arid inland river catchment in northwest of China, facing the challenges of reasonable groundwater exploitation and retarded groundwater disaster. Previous studies on surface water evaporation in the catchment did not consider the spatial heterogeneity and main control factors, which limits deep understanding of the evaporation process under the background of climate change. In this paper, based on time series, correlation and multiple regression analysis, the variation characteristics and main affecting factors of water evaporation in the upstream, midstream and downstream of the catchment are analyzed. The results show that (1) the water surface evaporation in the basin shows a fluctuating downward trend, but the spatial difference is obvious: 183.2 mm decreased in the upstream mountainous area in recent 60 years, 1135.1 mm decreased in the middle reaches in recent 60 years, and 241.7 mm decreased in the downstream terminal lake in recent 30 years. (2) The main controlling factors of water surface evaporation are different in the catchment: the main controlling factor is temperature in the upstream mountainous area, wind speed in the middle reaches, and water area in the terminal lake. (3) The climate change in the catchment is generally warm and humid, which is consistent with the global climate change. However, water evaporation does not increase with climate change, i.e., showing the “evaporation paradox” phenomena. The results indicate that great attention should be paid to the spatial differences and the main control factors, which have important influence on the evaporation research and water resource evaluation in arid areas.