Abstract:This article calculated the Z index by using the monthly 〖JP2〗precipitation data over the Songhua River〖JP〗 Basin from 1961 to 2017, and also analyzed the climatological characteristics and interdecadal variations of the summer rain waterlogging over the Songhua River Basin and the relationship with the climate system index. The results are as follows. Waterlogging tends to occur most in the main stream of the Songhua River in summer (12 in 30 years), 〖JP2〗then in the upper reaches of the Nenjiang River (11 years), and the least in the Xiao Hinggan Mountains area (7 years). However, 〖JP〗the Xiao Hinggan Mountains have the highest intensity of waterlogging (average 2.1 a-1), followed by the upstream of Songhua River (1.8 a-1), and in Zhangguangcai Mountains it is the smallest (1.4 a-1). The waterlogging occurs most in June in the Songhua River Basin, and least in August. The average rain intensity of waterlogging is the highest in August and the smallest in July. In the summer and July of 1961-2017, the waterlogging over the lower reaches of the Nenjiang River gets weakened significantly. In June, the intensity of waterlogging in the Xiao Hinggan Mountains increases apparently. The summer waterlogging events in the Songhua River Basin are affected by atmospheric circulation and oceanic factors during the previous period.