The present invention relates to a fully decoupled electro-hydraulic braking system, which comprises a booster motor, a booster transmission assembly, a brake master cylinder, a hydraulic control unitHCU, a normally closed solenoid valve A, a brake pedal, a pedal push rod, a human hydraulic cylinder, a two-position three-way solenoid valve, a pedal sensing simulator, a fluid reservoir, a normallyclosed solenoid valve B, a pedal stroke sensor and an electronic control unit ECU. The invention has three working modes of conventional braking, active braking and failure backup. The invention eliminates the structure of the high-pressure accumulator, adopts the motor driving and the mechanical structure driving, and has the advantages of simple structure, more reliable work, faster response speed, more accurate pressure control, and lower cost and maintenance cost. The invention adopts the scheme of complete decoupling, and can precisely control the hydraulic braking force through the booster motor, cooperate with the regenerative braking to recover the braking energy to the maximum extent, improve the range and comply with the development trend of the automobile electricization.