Abstract: Based on the data obtained from 10 meteorological stations on Tianshan Mountains during 1961-2006, the fundamental change characteristic of annual average temperatures, annual precipitation were analyzed, and the natural vegetation net primary productivity (NPP) in nearly 46 years of Tianshan Mountains were calculated using the net primary productivity models for natural vegetation made by ZHOU Guangsheng and ZHANG Xinshi. Statistic relations between NPP and annual average temperatures, annual precipitation were constituted, and the effect of future climate on NPP was estimated. The main results showed that in 46 years, annual average temperature increased at 0.029 ℃/a; annual precipitation variations increased at 1.38 mm/a; natural vegetation net primary productivity increased at 0.013 t/（hm2a）. The climate turned to be warmer and humid at the beginning of 1970s and accordingly, natural vegetation net primary productivity had a sudden increase. This kind of climate change in the future will have a positive effect on natural vegetation net primary productivity in Tianshan Mountains. Averagely, if annual average temperature elevates every 1 ℃ or annual precipitation increases every 10%, the NPP will increase 4%-5% if other conditions invariable.