Abstract: The ratio of the skewness coefficient to the variation coefficient is computed with uniform method for the rainfall data from 5 100-13 600 stations with durations of 10-min-3-day and 210 stations with durations of 1-day-90-day and 1-year.The ratio of skewness to variation (R_sv) characteristics of the Pearson type Ⅲ frequency distribution are approached; the regional distribution of R_sv and the R_sv-duration relation are analyzed,and the same affected factors on R_sv are studied.On the condition of the data at present,the single R_sv value of 3.5 is not suitable for each region and each duration in rainstorm frequency analyses.