The invention discloses an electric hydraulic power-assisted steering system. In the system, a hydraulic pump pumps oil in an oil storage tank and outputs pressure oil to the pressure oil duct of the steering system; a pressure retaining valve comprises a pressure retaining valve core and a pressure retaining valve housing which are coaxial with the input shaft of a steering wheel and are nested with each other; the oil inlet of the pressure retaining valve is communicated with the pressure oil duct of the system; the oil return port of the pressure retaining valve is communicated with the oil storage tank; chambers on the two sides of the piston of a double-action power-assisted cylinder are respectively communicated with the two control oil ports of the pressure retaining valve; the piston of the double-action power-assisted cylinder is connected with the input shaft of the steering wheel through a transmission mechanism; the oil port of an energy accumulator is communicated with the pressure oil duct of the system; a detector is used for acquiring steering parameter signals and outputting the steering parameter signals to a control device; and the control device receives the steering parameter signals acquired by the detector, and determines whether to output a control signal to the electric drive device of a hydraulic pump according to the preset conditions. The invention also provides an automobile utilizing the electric hydraulic power-assisted steering system and a control method thereof.