Based on the data of daily mean temperature and precipitation from 96 meteorology stations in Southwest China and the ERA-20C reanalysis daily data from 1961 to 2014,using the method of REOF,the surface humidity index (SHI) and modified surface humidity index (MSHI) were calculated in order to study the time and space distribution characteristics in Southwest China. The following conclusions can be drawn: (1) looking from the first four models of REOF,the soil moisture has decreased in the 50 years in Southwest China,except for the western Sichuan Plateau,especially obviously in the Sichuan Basin and southern Yunnan-Guizhou Plateau. (2) according to the result of REOF space modals,climatic division in Southwest China was able to present; based on different climatic divisions and monthly average precipitation,the surface humidity index (SHI) could be improved to modified surface moisture index (MSHI),as a result,both SHI and MSHI had certain similarities in annual precipitation on space distribution: low index area in accordance with the weak precipitation area, northwest being relatively dry,Yunnan-Guizhou Plateau being relatively moist in the south. (3) looking from the spatial distribution,MSHI was closer to the rainfall distribution than SHI; moreover,its spatial continuity was better; looking from the time series,compared with SHI,MSHI can reflect drought years better in Southwest China. This study has important significance for water resource utilization and understanding climate change in the future.