Abstract: To enhance filtering effectiveness and to reduce design complexity, we propose a pre-filter design that can be incorporated into 2-DOF PID control systems. During the design process, the component system response output is analyzed and then, based on the least squares method, a pre-filter method for enhancing the system response property is devised. The resultant pre-filter has a simple PID form and is convenient for use in 2-DOF PID control system construction. There are several significant advantages to the proposed design: system identification is not needed, the whole design process only requires system output signals, the designed pre-filter can effectively eliminate the vibration of the system output of 2-DOF PID control system in step response, and the response speed of the designed system is consistent with that of the pre-set reference model. Through simulation of the design of the pre-filter for a typical PID control system, we obtain the response output signal based on the pre-filter design process. The filtering effectiveness is then tested by simulation and the results prove the pre-filter's effectiveness.