Taking a turbine driven pump system as the research object, modal reduction suitable for multi-stage geared rotors system was proposed.A dynamic model of the system was established by the finite element modeling method.And the degree of freedom of the system was reduced by the modal reduction.Based on this, inherent characteristic, steady state response due to mass unbalance and static transfer error, transient response in start-up state, and transient response when sudden unbalance occurs under steady operation were studied.Results show that the reduced model still has higher precision than the original model in calculating natural frequency and steady state response of the system.Static transfer error excitation can excite high order modes of the system in low rotation speed range.To ensure the calculation accuracy, the certain number of degree of freedom should be retained when calculating the response caused by the static transfer error excitation.When calculating the transient response, the reduced model saves more than 90% of calculation time compared to the original model, and deviation is small.In summary, the proposed modal reduction greatly reduces calculation time while ensuring calculation accuracy, and provides an efficient and reliable method for accurate prediction and analysis of the dynamic characteristic of the multi-stage geared rotors system.