The invention relates to a regenerative braking energy recovery system of a serial hydraulic electric vehicle. The regenerative braking energy recovery system comprises a battery, a motor, a first variable displacement pump, a drive axle, a first fuel tank with a second variable displacement pump, a second fuel tank with a third variable displacement pump, an energy accumulator, a flywheel and a braking ECU (electronic control unit), wherein the battery is electrically connected with the motor, the motor is connected with the first variable displacement pump through a first clutch, the first variable displacement pump is connected with the second variable displacement pump through a pipeline and is also connected with the third variable displacement pump through a pipeline, and the energy accumulator is connected with the second variable displacement pump through a pipeline; and the second variable displacement pump is connected with the drive axle, and the drive axle is connected with the vehicle through a transmission; and the third variable displacement pump is connected with the flywheel through a second clutch. The regenerative braking energy recovery system has the beneficial effects that excessive energy produced in system braking can be stored, certain energy can be released when needed, the pressure stabilizing effect can be achieved for the whole vehicle, and energy recovery and reuse can be realized.