A compound sewage discharge valve relates to the discharge valve field, comprising a valve body, a valve cover, a vent cap, a connecting rod, a floating ball and a piston mechanism, wherein said piston mechanism comprises a piston main shaft penetrating into a guide sleeve, a gasket ring provided below the piston main shaft, a piston arranged in the piston main shaft above the valve cover, and a top plug provided in the valve cover. The valve is characterized in that the piston main shaft is provided with a spring that is arranged horizontally with a piston main shaft in one end and a sealing element in the other side. The sealing element is propped against the inner wall of the valve cover discharge pipe. The invention is simple in the structure and rational in the design. The piston and the top plug seal primarily while the sealing element and the vent hole seal secondarily. As the spring element has many gaps, the reliability of sealing is increased without affecting the exhaust effect and leakage is reduced.