The invention relates to an automobile composite braking system, comprising a hydraulic braking subsystem and a motor braking subsystem, wherein the hydraulic braking subsystem is composed of a pedal brake valve, a pressure retention mechanism, a pressure regulating mechanism, an ABS/ESP hydraulic valve block and a braking controller; the P port of the pedal brake valve is connected with the oil circuit at the outlet of a high pressure accumulator, the T port thereof is connected with the oil circuit of a liquid storage pot, and the A port is connected with the oil circuit of the pressure regulating mechanism; the pressure regulating mechanism is connected with the ABS/ESP hydraulic valve block and the oil circuit of the liquid storage pot; the braking controller is connected with the pressure regulating mechanism, a braking pedal displacement sensor, a wheel speed sensor and a pressure sensor circuit on the oil circuit; and the motor braking subsystem is composed of a motor, a derailleur, a motor controller and batteries. The pressure regulating mechanism can be formed by a two-position two-way normally closed valve and a normally opened valve, and also can be an independent tri-way normally opened electro-hydraulic proportional valve. The motor braking subsystem is supplied with braking force from the hydraulic braking subsystem when braking force thereof is insufficient. The invention can be used in a hybrid electric vehicle, a pure electric vehicle and a fuel cell electric vehicle.