Abstract: Based on the 160 observ ational station's dat a of monthly precipitation and mean monthly temperature over China from 1951 to 1997,by use of the surface humid index computed from the data,Hi=P/Pe(P is the monthly total of precipitation,Pe the potential evaporation from air temperature),the interannual variation,decadal variation and the seaso nal differences of the sur face humid index,precipitation and temperature over two ty pical drought regions,the northwestern and northern China,have been analyzed.The geogr aphical distributions and trends of surface humid index have been given in the areas.The results indicated that the interannual and decadal variation of surface humid index over northren China is contrary to that of the west region of north western China,the form ershowed the wetting trend,and the latter drying trend.Also,the results show ed that the drying trend of northern China generally occurred in summer and autumn,and that the wetting trend occurred in various seasons in northw estern China except for autumn of the east region of nor thwestern China,and summer of westregion of northwestern China.