Because of the influence of the structural parameters of the pump shaft transmission system on the dynamic and static performance of the plastic centrifugal pump, according to the structural parameters of the centrifugal pump, the three-dimensional model of the impeller and volute chamber was drawn. The composition of radial force and axial force generated when the plastic centrifugal pump works were analyzed. The CFD calculation of the load of the plastic centrifugal pump was carried out. The flow field of the plastic centrifugal pump under ideal working conditions was simulated by ANSYS FLUENT. Combined with the application principle of singular function in mechanics, the mathematical model of the deflection of the pump shaft transmission system was constructed. And the key factors affecting the deflection of the pump shaft were analyzed. Taking the minimum deflection and the maximum critical speed of the first order as the objective function, the constraint conditions were determined by the geometric relationship, and the optimization model of the structural parameters of the pump transmission system was established. The NSGA-II multi-objective optimization method was used to solve the optimal structural parameters of the optimization model, and the optimization design of pump shaft span, cantilever, front and rear bearing clearance was completed. The optimal span cantilever ratio of the rotor model of the single-span cantilever structure was 1:0.75. The ZT-3 rotor test device was used as a platform to verify the effect of span and cantilever ratio on the dynamic performance of the rotor.