This paper presents an ESO-based iPI control for common rail pressure. First, a detailed mathematical model of High Pressure Common Rail Injection System (HPCRIS) is built. The mathematical model is validated by the software Matlab and commercial software AMESim. For the considered HPCRIS, an effective model free controller which is called Extended State Observer - based intelligent Proportional Integral (ESO-based iPI) controller is designed. And this proposed ESO-iPI controller is composed mainly of the referred ESO observer, and the iPI controller. Finally, to demonstrate the performances and effectiveness of the proposed controller, the proposed controller is implemented and compared with a conventional PID controller and Active Disturbance Rejection Control (ADRC), and their corresponding simulations are carried out.