The invention belongs to the technical field of aircraft brake system design, and relates to a pressure regulator of an aircraft hydraulic brake system. The pressure regulator comprises a shell (1), abush A (2), a pressure reducing and flow splitting valve (3), a spring B (16), a first sleeve (17), a fixing seat (20), a spring assembly, a piston assembly, a flow splitting control valve (32), a guide sleeve B (44), a piston rod (43) and a second sleeve (38). According to the pressure regulator, the control pressure comes from the outlet pressure, a main valve core is of an open type, a main valve is operated through the oil inlet pressure, the outlet pressure is introduced into a lower cavity of the main valve and then enters an upper cavity of the main valve through damping holes in the main valve core, the liquid discharging pressure of the main valve core and the operating force of an upper piston are balanced by the spring force, the operating force is applied to a pilot valve, oilliquid in an oil inlet enters an upper cavity of a piston of the main valve core and changes the pressure of the upper cavity of the piston of the main valve core, so that the outlet pressure is adjusted.