In this paper, investigation and analysis on the operation of 3 combined wastewater treatment plants in sunny and rainy days in Wuhan city was made. The operations of lifting pumping stations in these plants were inspected. During sunny days, the processing units and equipments in these plants run in nearly full load and the load can only increase in a small quantity in rainy days. But the total waster water quantity in Wuhan in rainy days would reach to ten times more than wastewater quantity in sunny days. A large amount of untreated wastewater overflows from the channels to the bodies and causes heavy pollution to the water environment.