Abstract: Based on RS and GIS, 11 indexes from three aspects including natural capital, social pressure and economic supports were selected. The natural capital index (NCI), social pressure index (SPI), economic support index (ESI), and environment quality evaluation index (EQEI) were constructed by using spatial principal component analysis, variation coefficient method, and analytic hierarchy process. The spatial distribution characteristics and influencing factor of the environmental quality in Shiyang River Basin were analyzed. The results showed that the overall environmental quality was at poor level in Shiyang River Basin. The regions with better classes of environmental quality were mainly concentrated in the upper reaches of Qilian Mountains, and those with poorer classes were mainly concentrated in the middle-lower reaches of low hills land and desert. The EQEI value in Shiyang River Basin had polarization phenomenon from southwest to northeast. With the variation of distance, the value had large variation range, with obvious spatial heterogeneity. The environmental quality showed both high and low aggregation patterns, with "fault" distribution. There were highly clustered hot spots and highly clustered cold spots in the basin. Among the influen-cing factors of environmental quality, natural capital was the dominant one, social pressure was the second, and economic support was the least contributor.