An oil suction pump contains: an oil storage cylinder, a pumping mechanism, and a cap. The pumping mechanism includes a body, a drive rod, a plug, and a pressure relief valve. The cap is disposed on the body and the oil storage cylinder, and the cap includes a connector. The drive rod has a press lever, the cap further includes a first air conduit, a first one-way valve assembly, and a second air conduit. The second air conduit has an inlet segment, an outlet opposite to the inlet segment, and a pump segment defined between the inlet segment and the outlet segment and communicating with the oil storage cylinder. The cap further includes a second one-way valve assembly accommodated in the oil storage cylinder and connected with the pump segment, and the second conduit accommodates a pressure reducing valve.