In flight test, the aircraft will produce mixed combustible gas, and the change of gas concentration will bring great security risks to flight test safety. In view of the limitations of traditional test methods, such as long response time and low accuracy, the new aircraft and new mission put forward higher requirements for gas concentration test. According to the requirements of the model task, through the analysis of the test environment, gas composition and current gas concentration measurement technology, the overall technical scheme of mixed gas concentration test is determined, and a new airborne mixed combustible gas concentration test system is developed, which realizes the real-time and high-precision measurement of gas concentration. This paper mainly expounds the principle and design scheme of the test system, and introduces in detail the background noise removal technology based on time division multiplexing. The ground and flight tests are carried out respectively. After data analysis, the system is stable and functions normally, and all indexes of the test data can meet the requirements of the model task test.