The invention provides an oil pump. One end of a valve body is provided with an air inlet, a liquid sucking opening, a liquid spraying opening and a gas path, wherein a plunger compartment extends inwards along the air inlet, a plunger is arranged in the plunger compartment in a sliding connection manner, a return baffle is arranged between the air inlet and the plunger compartment, an advancing baffle is arranged at the bottom of the plunger compartment, and a return spring is arranged between the plunger and the distal end surface of the plunger compartment; the liquid sucking opening is arranged at the distal end of the plunger compartment, is connected with a pipette and is internally provided with a steel ball; the liquid spraying opening is arranged at the distal end surface of the plunger compartment and is communicated with an outlet at the other end of the valve body, a steel ball and a spring are arranged in the outlet of the liquid spray opening; and an inlet of the gas path is arranged between the back baffle and the plunger in contact with the advancing baffle plate, and an outlet of the gas path is arranged on the outer side of the liquid spraying opening. The oil pump disclosed by the invention has the beneficial effect of simple and reliable structure, and the outlet firstly sprays quantitative liquid and then sprays compressed air when the compressed air is charged into the air inlet.