Change of runoff and climate in mountain watersheds of Kaidu river and Urumqi River originated respectively from the south slope and the north slope of the Tianshan Mountains was analyzed based on the past 50a observational data at relevant hydrological and weather stations, and the various climate scenes were assumed and the response models of mountain runoff to climate change were established to analyze sensitivity of runoff to climate change. The results are as follows. Variations of temperature, precipitation and runoff in the study area have been presenting an oscillating and rising trend as a whole since 1960s, and the rising range is quite obvious after 1990s. There is a markedly  positive correlation between Mountain runoff and temperature, precipitation on the one hand, and there are also some regional differences in response degree of mountain runoff to precipitation and temperature on the other hand. The mountain runoff of Urumqi river basin is more sensitive to precipitation change than that of Kaidu river basin and the mountain runoff of Kaidu river basin is more sensitive to temperature change than that of Urumqi river basin.