The utility model discloses a single-vane vacuum pump for an engine, which is used for solving the problems that the vacuumizing efficiency of a vacuum pump is reduced due to defects of an oil discharge tank. According to the technical scheme, the single-vane vacuum pump comprises a pump body, an end cover, a rotor and a vane, the rotor and the vane are positioned in the pump body, the single-vane vacuum pump is characterized in that an independent oil discharge tank is arranged on the pump body and positioned at the end cover close to the side wall of the pump body, and the position of the oil discharge tank corresponds to an oil discharge outlet arranged at the bottom surface of the pump body. Due to the structural design of the oil discharge tank, not only can excessive lubricating oil be enabled to flow back from the oil discharge tank, the counter acting force of the lubricating oil to the vane can be greatly reduced, but also excessive pressure can not be discharged while oil is discharged, and the vacuumizing efficiency of the vacuum pump can not be basically reduced; the vacuumizing efficiency of the vacuum pump can not be influenced while the working reliability of the vacuum pump is ensured, and the defects that the vacuumizing efficiency is reduced due to large volume of series notches of the oil discharging outlet can be completely solved. In addition, the processing difficulty can be lowered according to the position of the oil discharging tank.