Using the surface temperature data of 27 urban observation stations and 65 country contrastive stations over Northwestern China during 1961-2000,the urbanization effects on different scale cities were checkup.The results showed that there were two sorts of urbanization effects,namely positive and negative effects,and the urbanization effects ranged from -0.41℃ to 0.69℃ during 1961-2000,the urbanization effects contribution to temperature warming ranged from 5.3% to 27.7%.The intensity and stability of urbanization effects nearly related with the city size.In general,the big cities had the biggest intensity and the highest stability,middle cities followed it,small city had the least stability and its intensity easily changed with temperature fluctuating.Moreover,the urbanization effects were different during different periods,the average urbanization effect over Northwestern China in 1961-2000 was 0.02℃,-0.01℃ in 1981-2000,and 0.24℃ in 1991-2000.As a whole,the urbanization effects have a little influence on temperature warming over Northwestern China,the dominant fact on temperature warming was still naturally environmental changes.