The invention discloses a two-stage oil pump which comprises a driving gear (1), a main pump body (2), a safety valve component (3), a main pump braking gear (4), a main pump fixing bolt (5), a main pump positioning pin (6), an auxiliary pump body (7), an auxiliary pump fixing bolt (8), an auxiliary pump positioning pin (9), an auxiliary pump braking gear (10), a pump cover (11), an auxiliary pump driven gear (12), a main pump driven gear (13) and a pressure-limiting valve (14). According to the design, a main pump is used for providing normal pressure oil for an engine, the auxiliary pump is used for pumping oil at the higher position of the inner chamber of an oil bottom casing into the lower position of the inner chamber of the oil bottom casing, so that the oil surface at the lower position can be kept with the stable height and reaches the oil pump, the crank throw of a crank shaft and the big end of a connecting rod can be operated normally.