In recent years, the greenhouse effect has become more and more obvious. The side effects brought by increasing of CO₂ concentration have seriously affected people's production and life, and are even closely related to everyone's healthy. In defect of the large size, portability, high precision, and modularity of CO₂ commercial sensors currently, a pyroelectric-based non-dispersive infrared (NDIR) method measuring CO₂ concentration system was designed. The system design was mainly divided into four parts: air chamber structure design, signal circuit design, software control design and data processing. The air chamber structure design adopted a single-channel structure design, which was optically simulated. Finally, the size of the air chamber was determined, which effectively improved the measurement accuracy of the system. In terms of signal circuit design, a small signal amplifying circuit based on the differential method was designed to extract and amplify the effective signal from the noise to increase resolution. The software control design employed digital filtering algorithm to filter out interference and clutter, extract the effective value in the data, and improve the signal-to-noise ratio. In view of data processing, a gas test platform was built, and the temperature and humidity and peak-to-peak compensation formulas were used to compensate for the influence of temperature on the peak-to-peak value. Then, the gas concentration value was calculated using the curve fitting method at 25 ℃, and finally output through the serial port. After testing, the measurement range of the system is 5%, and the relative error is within 1500 ppm, which can meet the safety requirements of fire alarm, underground and other occasions monitoring.