The different level rainy days and its homologous precipitation quantity are obtained by using the daily precipitation data from
May to September ( 1960 － 2004) of 17 stations in the Qilian Mountain area，thus，we know the daily precipitation intensity of light
rainfall and moderate rainfall( and more) at each station． Based on regional mean value of the different level rainy days and rainfall intensity
in Qilian Mountain area，the tendency of the different level rainy days and rainfall intensity was analyzed using linear trend coefficient
and 5 levels main value function． The results show that both precipitation and different level rainy days from May to September
in Qilian Mountain area presented more in the west side and less in the east side in the same latitude area，and more in the east and
less in the west part of Qilian Mountain． In recent 45 years，the light rainfall days was descending，but the moderate rainfall days was
ascending． The precipitation intensity of light rainfall and moderate rainfall ( and more) presented ascending trend too from May to September
in Qilian Mountain area． The morlet wave analysis show that the light rainfall days had a period of five years，but the period of
the moderate rainfall ( and more) days was more complex．

Using daily p recip itation data in 59 stations of Gansu p rovince during 1960 - 2006, extremely heavy p recip itation thresholds  are determined for different stations, and the temporal and spatial distribution of summer extremely heavy p recip itation is diagnosed in recent half century. The results show that the consistent anomaly distribution is main spatial mode for summer heavy p recip itation in Gansu p rovince, and the spatialmode is divided into five key areas: the Longnan area, the Longzhong area, the west of Hexi area, the east of Hexi and the Longdong area, respectively. The extremely heavy p recip itation p resented decreasing tendency in the Longnan and Longzhong areas, and increasing tendency in the east of Hexi and Longdong areas, but it came through few - more - few change in the west of Hexi area. From period analysis, the period vibration of 11 - 13 a and 6 - 8 a disp layed clearly in most key areas.

The average beginning and ending period of rainy season in Northwest China was analyzed by using the precipitation data of ten
days by ten days from 131 stations in Northwest China and monthly height grid data of 50 x 100at 500 hPa over Northern Hemisphere from
1960 to 2000 and the relationship between precipitation and 500 hPa height field was analyzed by SVD method in rainy season. The re-
sups show that the rainy phase is from May to September and the distribution style of the beginning and ending period of rainy season is
、omplex} but the first ten days in July to the first ten days in September、an represent the rainy season in  main precipitation area.  The
precipitation in rainy season not only has relationship with the same一period 500 hPa(irc;ulation but also with the previous periods 500 hPa
(irc;ulation from March to May and from December to February but the key areas effected by different period(irc;ulation is great different

A heavy rain and hail event occurred in Zhangxian county from 16：20 to 19：10 on July 22，2003.Starting from the circulation background of large scale，and using diagnostic analysis of physics quantities，we discussed the main causes of the heavy rain.The results show subtropical high towards northwest，cold wave from north towards south，lower-trough and shear of Qinghai-Xizang plateau are the main circulation background of this event.By analyzing the three-dimensional contruction physics field of the circulation，it shows physics field has leading value to forecast nearly heavy rain