In order to effectively prevent harmful gas from dangerous chemical environment from entering the cabin from the gap of the vehicle cabin, the method of driving the fan to add purified air to establish overpressure in the cabin is adopted, and the over-pressure measurement and control system based on STM32 single-chip microcomputer is designed. The system uses the MQ135 gas sensor as an example to collect the information of the harmful gas (carbon monoxide, etc.) outside the cabin as the trigger signal of the STM32 controller. The pressure sensor collects the pressure difference between the internal and external pressure of the cabin, and uses the incremental PID algorithm to output the PWM wave to realize the closed-loop control of the fan. The amount of purified air is greater than the amount of air in the gap in the cabin, and an overpressure environment is established to ensure a single flow of air source to prevent harmful gases from entering the cabin. The system housing shielding analysis design, the digitization of the sensor improve the reliability of the system in the vehicle electromagnetic environment, and the modular design increases the interchangeability of the system. After in-cabin testing, the feasibility of the system to detect harmful gases outside the cabin to stabilize the establishment of an overpressure environment was verified.