Upper reaches of Yellow River have been one of the worst-hit areas of land desertification and of the key areas of desertification monitoring and handing operation in China. Based on RS and GIS technologies, the authors used artificial visual interpretation method and the field survey to obtain interpreting data for 4 periods by MSS-, TM-, ETM- and CBERS images. The authors studied the situation and distribution of desertification and the space-time evolutionary process in the upper reaches of the Yellow River from 1975 to 2007. Then, with the regional air temperature and precipitation data,the authors analyzed their relationship with the evolutionary process of desertification. The results showed that the desertification of the upper reaches of Yellow River increased 3 499. 76 km~2 totally from 1975 to 2007, thereinto, sandy desertification area increased 3 407. 62 km~2 and the saline desertification area increased 92. 14 km~2. The development trend of the desertification firstly increased and then decreased from the three stages. The desertification increased before 2000 and decreased after 2000. Combined with the analysis of temperature and precipitation data,it was considered that the climatic change was one for the important reasons for the development of land desertification of the upper reaches of Yellow River, and its geological background was the internal cause and human activity was the catalytic role.