The mathematical model was established for the closed hydraulic system of the main lifting mechanism of 4 000 t large crawler crane. The parameter setting of the centralized charge system was analyzed under different working pressures and input speeds of system. The matching relationship between the displacement of the centralized charge system and the flushing valve was determined under the maximum system working pressure. The effects of quantitative centralized charge system and variable centralized charge system were compared on the pressure and oil temperature of the system low pressure chamber.It provides theoretical basis for the parameter setting and selection of centralized charge system.