Disclosed is a large-scale submersible sewage pump assembly that includes a pump and a pump seat installation structure, wherein the pump seat installation structure has a concrete installation base layer, and a pump seat for installing the pump. The pump seat is fixed to the pump installation layer, and the bottom of the pump is directly connected onto the pump seat. The pump has a motor cooling apparatus, wherein the cooling apparatus has an internal cooling apparatus installed inside the case of the motor, and an external cooling apparatus installed outside the motor. The pump seat installation structure can stably mount and support the large-scale submersible sewage pump, preventing potential safety hazard during running of the pump.