The invention discloses a design method for interference fit between an engine gear and a shaft. The design method comprises the steps of S1, clearing the basic size, the material parameters, the junction surface roughness, the working temperature and the assembly mode of the gear and the shaft; S2, calculating the minimum magnitude of interference; S3, calculating the maximum magnitude of interference; S4, determining the selection range of the magnitude of interference between the gear and the shaft; S5, analyzing and evaluating whether the calculation result meets the expected design index or not; and S6, determining the magnitude of interference between the final gear and the shaft, and designing the size and the tolerance of the gear and the shaft. According to the design method for the interference fit of the engine gear and the shaft, the optimization design of the interference fit of the gear and the shaft can be simply and efficiently completed, and the design period is shortened, the design cost is saved, so that the design of the engine parts is better achieved.