The invention relates to the technical field of agricultural mechanical equipment, and provides a plunger pump for an agricultural machine. The plunger pump comprises a plunger pump shell, a rear cover is connected to the rear side wall of the plunger pump shell in a penetrating manner, an oil inlet and an oil outlet are formed in the rear cover, an oil supplement pump cover is connected to the rear side wall of the rear cover, a transmission shaft is arranged on the inner side wall of the plunger pump shell, a cylinder body is meshed on the section, located in the plunger pump shell, of the transmission shaft, a flow distribution plate is propped against the rear side wall of the cylinder body, a plurality of plunger holes are formed in the cylinder body, and plungers are connected in theplunger holes in a sliding mode. The plunger pump has the advantages that the defects in the prior art are overcome, the design is reasonable, the structure is compact, the problems that the displacement of an existing plunger pump is not easy to adjust, the strength is not high, the protection measures are incomplete, and the pump is not prone to be connected in series are solved; and a simple structure combination is adopted by the plunger pump, the displacement can be conveniently and quickly adjusted by rotating a adjusting rotating shaft, meanwhile, the strength and the protection measures of the pump are improved, the pump is more suitable for being connected in series, and a strong practicability is achieved.