A pump structure of a portable oral irrigator, the oral irrigator main engine comprises a housing and a pump assembly； the pump assembly is disposed within the housing and is provided with a pump body, a driving motor, a water outlet provided corresponding to the water outlet nozzle, and a water inlet provided corresponding to the water inlet nozzle are disposed on the housing； an output shaft of the driving motor is drivingly connected to the pump body by means of a spur gear and a contrate gear； the pumping piston head is disposed in one end of the pump cylinder, and the other two ends of the pump cylinder are communicated with the water outlet nozzle and the water inlet nozzle； one end of the piston rod is connected with the pumping piston head； and the other end of the piston rod eccentrically and rotationally cooperates with the contrate gear.
