Abstract: This paper mainly analyses the pattern of the variation of rainstorm days at east part of the Hexi Corridor，Gansu Province，China from 1961 to 2012 by using linear regression analysis，Mann-Kendall method，and wavelet analysis method. The results show that the average number of rainstorm days was 1.2 d·a-1 at the eastern part of the Hexi Corridor，and it mainly was local rainstorm within the region. The temporal and spatial distribution of rainstorm days vary considerably: the number decreases rapidly southward and eastward. The most intense rainstorm mainly occurs at the Gulang County located in the windward slope of the Qilian Mountains. The number of rainstorm days has an annually increasing trend in general，and the liner tendency rate is 0.24 d·（10 a）-1. The most one occurs in the 2000s century with 15 days of rainstorm，while the least one occurs in the 1980s with only 6 days. The sub-regional rainstorm has the opposite trend with the regional rainstorm in the period of the most one and the least one. The variation of monsoon has a significant impact on the number of rainstorm days，which results in rainstorms frequently occur in June to August. The number of rainstorm days within these months account for 90.3% of the whole year rainstorm days. Among which August has the largest number of rainstorm days accounting for 48.8%. The rainstorm mainly occurs in the daytime. Using Mann-Kendall method，the number of rainstorm days at the east of Hexi Corridor has been increasing since 1963 and from 1985 to 2013，the number increases significantly. Warmer weather may be one of the causes for the increasing extreme precipitation frequency. Wavelet analysis method shows that the number of rainstorm days has a nine-year and a six-year period. The regi- onal yearly precipitation has a similar varying trend to the number of rainstorm days，which indicates that the inc- reasing days of extreme raining may cause the yearly precipitation to increase as well. Based on the NCEP reanalysis data from 1983 to 2012 nearly 32 years，the upper air circulation of rainstorm has been summarized as the west-southwest flow type of the western subtropical high and the blocking high type in Hetao area，while a large class rainstorm happened in the type of the blocking high in Hetao. Threshold of physical elements of occurrence of rainstorm has also been calculated by analyzing the physical mechanism of rainstorm happened in Hexi Corridor.

Key words: rainstorm, temporal and spatial distribution, circulation characteristics, physical quantity threshold, eastern Hexi Corridor