Snow cover is one of the sensitive factors to climate change in arid area. There is a close relationship between snow cover days and snow cover area. In order to analyze the spatial distribution of snow cover days, eight-day synthetic data of MODIS from Terra (MOD10A2) and Aqua (MYD10A2) were used. Firstly, the snow cover days (500 m x 500 m) in Tianshan Mountains were obtained through removing the effect of cloud based on combined snow cover products of MODIS. Then, based on annual snow cover days and DEM data, the spatial and temporal variabilities of snow cover days with elevation and aspect from 2002 through 2014 were analyzed. The results show that the distribution of snow cover days had been extremely uneven. The maximum annual mean snow cover days were 193 days. The snow cover days in 83.92% area of the Tianshan Mountains had changed little during the 13 years. About 48% snow cover days was no more than 30 days. The snow cover days had increased with elevation, with a large spatial difference. More snow cover days (>30 d) were gathered in the north, northeast, east, west and northwest aspects. This study will be useful for estimating water resources in arid areas.