Perfluoroisobutyronitrile (C4F7N) has the potential to replace SF6 due to its excellent environmentally friendly dielectric properties, and has received extensive attention at home and abroad. C4F7N has a low liquefaction temperature, so it is necessary to mix it with low-boiling gas during application. Among them, the C4F7N/CO2 mixed gas has excellent performance, but the insulation capacity is closely related to the C4F7N content. Therefore, the preparation of high-precision C4F7N/CO2 mixed gas is conducive to scientific demonstration of C4F7N and minimizes the hidden dangers of industrial applications. Through the Fourier infrared detection platform, the infrared absorption information of C4F7N gas in the 500~4500cm-1 band was obtained, and the 1200~1300cm-1 band was determined as the key research object. A portable detection system for C4F7N/CO2 mixed gas is designed based on NDIR technology. As for the C4F7N gas sensor module, the low-power EMIRS50-AT06V standard blackbody light source with rugged MEMS design and the dual-channel detector with InfraTec LRM-202 narrow bandpass filter, combined with the gold-plated gas chamber structure of the reentrant light path, can effectively improve the detection accuracy of the system.Determine the inversion algorithm of the difference principle, and finally realize the fast detection of the C4F7N gas content. The experimental results show that the non-linear correlation between SB/SA (the ratio of the amplitude of the reference signal and the signal amplitude of the measurement channel) and the volume concentration fitting nonlinearity R2 is 0.99797. Within the range of the sensor, the maximum indication error is 1.05%, and the RSD of the sensor repeatability experiment is 0.47%, 0.36%, 0.31%, 0.34%, all of which do not exceed 0.5%, indicating that the sensor has good accuracy and consistency.The high integration and portability of the system can provide a novel method for the rapid online detection of the C4F7N/CO2 mixed gas mixture ratio of high-voltage electrical equipment.