The invention discloses an oil pump and a speed adjusting mechanism as well as a positive-negative correction mechanism thereof. The speed adjusting mechanism comprises a positive correction support, a negative correction support, a positive correction rod, a positive correction spring, a negative correction rod and a negative correction spring, the positive correction rod is arranged at the upper ends of the positive correction support and the negative correction support, two ends of the positive correction rod are erected on the positive correction support and the negative correction support respectively, the positive correction spring is arranged on the positive correction rod between the positive correction support and the negative correction support, the negative correction rod is arranged at the lower ends of the positive correction support and the negative correction support, two ends of the negative correction rod are erected on the positive correction support and the negative correction support respectively, and the negative correction spring is arranged on the negative correction rod between the positive correction support and the negative correction support. The positive-negative correction mechanism meets requirements on torque reserve of non-road vehicles and is simple in structure and positive-negative correction and adjustment process.