Abstract: 4 stations in Northwest China monthly mean maximum and minimum temperature and cloud from 1932 to 1992 were used to analyse and compare with Beijing. Eastern China and North Hemisphere. The results show that asymmetry is detectable in all seasons, the diurnal temperature range decreases. maximum -0.79℃/decade. There are Three kinds of asymmetry:①Tmax decreases, minimum -0.31℃/decade. Tmin increases, maximum 0.41℃/decade, in the eastern part of Northwest China (Xian and Lanzhou),② Tmax and Tmin decrease. but Tmax decrease more than Tmin, in The middle part of Northwest China (Anxi),③ Tmax and Tmin increase, but Tmin increase more than Tmax, in the northern part of Northwest China. The decrease of Tmax is mainly in winter, The increase of Tmin in summer, The decrease of daily temperature range is in all seasons, winter bigger than summer. The degree of asymmetric trend in Northwest China is bigger than Beijing. Eastern part of China and North Hemisphere. in which daily temperature ranges 1-4 times. The decrease of dai1y temperature range is partially related to increase in cloud. The maximum correlation coefficient is -0.92.