Due to the special structure of fullflow pump, the input mechanical power of the pump can not be measured directly, which makes it difficult to obtain the relevant characteristic parameters of pump device. To solve the problem that it was difficult to directly analyze the efficiency of pump unit, a loss separation method was proposed to calculate its efficiency. Based on the energy transfer between the motor and pump unit and the loss relationship, the motor input power and pump device related hydraulic parameters were measured,motor losses were separated from pump losses,the function curve fitting of the data was made with MATLAB, the input mechanical power of the pump was obtained, and the characteristic parameters of the pump in the fullpenetration pump were analyzed and calculated.Finally, formula analysis method was used to calculate the input mechanical power of pump unit.The deviation between them was compared.The results show that the loss separation method can be used to obtain more accurate characteristic parameters of the pump unit, and can be used to study the characteristics of full-flow pump unit test and to calculate and analyze the efficiency.