Based on the daily data of 7 meteorological stations in Altay region from 1961 to 2016, spatio-temporal change characteristics of ET_0 and meteorological factors were analyzed with climate change rate and inverse distance weighted interpolation method after calculation with the Penman-Monteith model. Then the multiple regression analysis method were combined with the correlation coefficient to study the causes of change of different time scales of ET_0. The results showed that the average annual ET_0 of Altay Region was 928.46mm, the climate change rate of annual ET_0 was -10.90mm·10y~(-1)(P<0.01). The seasonal average ET_0 from high to low was summer, spring, autumn and winter, summer ET_0 and autumn ET_0 showed a significant decrease trend(P<0.01), and winter ET_0 showed a significant increase(P<0.05). The maximum monthly average ET_0 appeared at June and July, the minimum value appeared at January and December, and annual distribution presented parabolic shape. Overall, the spatial distribution characteristics of ET_0 in difference time scales were basically consistent, and showed a significant decrease in ET_0 in the middle and west region, and the decrease in annual ET_0 was caused by the decrease of ET_0 in summer. The main contribution factor of different time scales of ET_0 change was different, but the significant decrease of average wind speed had the greatest effect on ET_0 reduction.