Abstract: The primary purpose of pressure regulating system is to regulate the pressure and flow rate of gas pipelines within the safe range. With its long-time operation and changes of downstream gas supply structure, many pressure regulating systems are no longer capable of normal pressure and flow control, and PID control gradually deflects away from new requirements. This paper introduces the composition and control principle of the pressure regulating system, expounds the traditional PID control principles and their shortcomings. Considering the supply requirement changes of long-distance gas pipeline, this paper presents the principle of approach control and its realization. This principle is believed effective to adapt to new regulating requirements and thereby meet the requirements of supply to downstream users.