The utility model discloses a combination valve of a first-stage pump and a second-stage pump. The problem that a liquid inlet valve plate and a liquid outlet valve plate swing or get stuck in the running process of the first-class pump combination valve is solved. In order to achieve the effects of reducing the failure rate of a combination valve and facilitating long-period stable operation of afirst-stage pump, the technical scheme is that the first-stage pump comprises a valve body, a liquid inlet valve deck is installed at one end of the valve body through a liquid inlet valve plate, anda liquid inlet valve spring with axial pre-tightening force is arranged between the liquid inlet valve plate and the liquid inlet valve deck in a sleeving mode; a drain valve cover is mounted at theother end of the valve body through a drain valve plate; drain valve springs with axial pre-tightening force are arranged in the drain valve cover and the drain valve plate; the liquid inlet valve deck and the liquid outlet valve deck are connected with the valve body through screws respectively, and the screws are in clearance fit with the liquid inlet valve deck and the liquid outlet valve deckso as to reduce swinging. And a plurality of liquid discharging through holes are uniformly distributed in the valve body relative to the central axis, so that the liquid inlet amount is more uniform.