The utility model discloses a compound servo braking system of electricity liquid all, it includes brake pedal, footboard return means, electronic helping hand assembly, master cylinder, liquid storage pot, master cylinder pressure sensor, hydraulic control unit, wheel cylinder, motor, ecu, brake pedal stroke sensor. Step on brake pedal, brake pedal's effort promotes the piston of master cylinder through push rod, reaction plate etc. Simultaneously, ecu calculates the helping hand size according to the signal of brake pedal stroke sensor, and the torque of control motor output through hold -in range and ball two -stage transmission, promotes reaction plate and ejector pin implementation helping hand, master cylinder brake pressure the most at last exports each wheel cylinder to through hydraulic control unit. The utility model has the advantages of it is following: the footboard sensation can design, ecu control motor output's moment of torsion can be passed through when the driver does not take to operate, active brake is realized, can realize the spare braking of manpower through stepping on brake pedal under the condition that the electronic control device became invalid.