The floods in Wuwei County are mainly consist of summer precipitation. In order to reveal the laws and characteristics of summer precipitation in Wuwei County for controling flood, reliefing drought and increasing crop production, the authors used the mathematical statistics method to study the laws and characteristics of summer precipitation change on multiple time scales including interannual, monthly, ten-day period, pentad, daily, daytime, nighttime, hourly, established a model to predict the precipitation in summer. The results demonstrated that there was a multi-cycle change law in the alternating current of abundant water and dry water in Wuwei county in summer precipitation. The first, second and third main periods are 10, 13 and 23 years, respectively. The summer precipitation is expected to be much rainfall stage and continue for a long time after 2016, but it is about to decrease. Within the year, the summer precipitation in Wuwei mainly concentrated in June and July, of which the last ten-day period of June and the first ten-day period of July took larger proportion. The precipitation presented a gradual increase from 1st, June, which peaked on 4th July and took a downturn afterwards. The concentration of summer precipitation in the past 10 years has shifted from June to July. From June to August, precipitation concentration has shifted from morning to afternoon and evening. Larger concentration of precipitation appeared between 6-7 o′clock in June, 5-6 o′clock and 15-18 o′clock in July, 17-18 o′clock and 20-21 o′clock in August, respectively.