A high-performance closed-loop control system based on FPGA was designed, which is used for regulating the gas flow of the main light source - optical pump terahertz gas laser in the polarization interferometer system of the tokamak device, in order to solve the problem of the output power decline of the traditional terahertz resonator after single inflation and long-term operation. The system’s hardware architecture employs a modular design, utilizing the MAX3232 level conversion chip to implement an RS-232 communication interface, which facilitates real-time pressure data acquisition from an APG200 capacitive vacuum gauge at a 1 kHz sampling rate. The core control module employs an enhanced anti-windup PID algorithm, allowing for seamless transitions between three stages—”pumping, intake, and pressure stabilization”—via a state machine. The output stage uses 12-bit high-precision PWM modulation (base frequency 20 kHz), which is converted into a 0–10 V analog signal through a fourth-order Butterworth low-pass filter (cutoff frequency 1 kHz) and an amplifier. This signal drives a Festo MPPES proportional valve and MFC to provide real-time compensation and precise control of the working medium and pressure within the terahertz resonant cavity. This system ensures the terahertz laser can sustain 24-h continuous stable operation, exhibiting outstanding dynamic performance and robustness, thereby offering reliable support for precision measurements in tokamak polarization interferometry.