To understand the scavenging effect of precipitation on PM_2.5 in Jiangsu-Zhejiang-Shanghai area, the precipitation and PM_2.5 observation data from 2014 to 2016 in 41 cities were analyzed. By comparing with the average concentrations of PM_2.5 between non-precipitation and full-time in two years, it is found that the former was significantly higher than the latter, showing that precipitation has a scavenging effect on PM_2.5 in this area. The ratio of PM_2.5 concentration before and after precipitation was used as the scavenging rate, while the ratio of concentration after precipitation and precipitation was used as the increasing rate. We studied the scavenging efficiencies of PM_2.5 at different periods, precipitations and precipitation durations in the target area. The results show that:(1) there is a positive correlation between scavenging ratio and pre-precipitation concentration of PM_2.5 in the northern part of Jiangsu-Zhejiang-Shanghai area, and the concentration of after precipitation are positively correlated with local emissions, which are different from the southern part of Jiangsu-Zhejiang-Shanghai area. (2) When the precipitation is 30 mm or the duration of precipitation is 36 h, the increase rate of the scavenging slows down, indicating that there is a threshold value for the PM_2.5 scavenging efficiency by precipitation.