Based on the 160 observational station's data of monthly precipitation and mean monthly temperature over China from 1951 to 1997, by use of the surface humid index computed from the data, H i=PP e(P is the monthly total of precipitation, P e the potential evaporation from air temperature),the interannual variation, decadal variation and the seasonal differences of the surface humid index, precipitation and temperature over two typical drought regions, the northwestern and northern China, have been analyz...