Abstract: In order to satisfy the demand of non-overload, submersible pump QS10 was selected as example to improve efficiency of centrifugal pump with low-specific-speed. Ten factors were carefully designed such as outlet width of impeller blade, inlet attack angle, blade number, inlet setting angle of guide vane, etc. 27 projects were decided upon L27(310)orthogonal test and the method of predicting multi-stage pump performance was studied. Based on analyzing the numerical simulation results of 2 stage models, the influence orders of geometry parameters on pump shaft power and efficiency were obtained. Results show that inlet setting angle of guide vane is predominant of ten factors affecting efficiency while blade setting angle is predominant affecting shaft power. And the optimal project selected after orthogonal test analysis was produced to test. The efficiency of designed point is up to 58.61% higher than the state regulation 51% and the maximum shaft power value is 3.83 kW complying with the design requirement of 4 kW, which verified the feasibility of the method of orthogonal design combined with numerical simulation in pump optimization design.