Abstract: Based on the daily rainfall data from 119 meteorological stations in Inner Mongolia region from 1971 to 2008, the climatic characteristic of rainstorm days was demonstrated by trend analysis, power spectrum analysis, wavelet analysis and mann-kendall test. A spatial distribution characteristic that the number of rainstorm days decreasing from southeast to northwest in the Inner Mongolia was observed and rainstorm days with higher amount of rainfall were found to frequently appear around the middle of July, the end of July and the beginning of August. There was the main period of 10 years and the secondary period of about 3 years of the rainstorm days. A mutation of the rainstorm days around the year of 1998 was encountered, and the average rainstorm days from 1979 to 2008 is 17.1 day shorter than that from 1971 to 1998.