Abstract: Electronically controlled hydraulic power steering (ECHPS) improves driver-s ‘road feel’ because it has alterable assistance character. Steering gear model and bypass ECHPS model were built based on the hydraulic principle of the control valve and ECHPS. A simple formula suited the two models was used to analyze the assistance character of steering gear and ECHPS. The bypass ECHPS parameters- affections were analyzed by changing basic gap- width or slot-s radius of the control valve, or torsion bar-s stiffness of steering gear or both of basic gap- width and slot-s radius. The electromagnetic valve- affection was also analyzed by changing the orifice-s figure of the spool. The results show that the assistance character of the bypass ECHPS is determined mostly by the control valve of the steering gear, it has relations with the electromagnetic valve else.