An FPGA-based field programmable gate array (FPGA) and wavelength-modulated tunable diode laser absorption spectroscopy (WM-TDLAS) technique have been combined to develop a programmable gate array WM-TDLAS CO₂ concentration detection system. Leveraging the programmable nature of FPGA chips, a digital lock-in amplifier (DLIA) with signal acquisition and modulation, as well as harmonic demodulation functions, was designed to meet the application requirements. To validate its performance, harmonic extraction tests, Q-factor assessments, and anti-noise experiments were conducted. The results revealed a linearity of 99.99% for the target frequency extraction and a Q-factor of up to 45. In the harmonic extraction experiments for signals with different signal-to-noise ratios, the maximum relative error in the mean value was only 0.91% when the signal-to-noise ratio was 43 dB. Using a distributed feedback laser with a center wavelength of 1572 nm as the light source, covering the absorption line at 6360 cm^?1, and utilizing an effective optical path of 14 m in a dense multi-pass gas absorption cell, gas concentration detection experiments were carried out. The system demonstrated a fitting linearity of 99.982% between the detected concentration and the amplitude of the second harmonic. By increasing the scanning wavelength frequency, the system was capable of obtaining concentration values in 0.1 seconds. The Allan variance results showed that the detection limit of the system was 1.86 ppm when the integration time was 44 seconds. The experimental results indicate that the developed WM-TDLAS detection system based on an FPGA array features high detection accuracy, rapid response, strong stability, and miniaturization, making it suitable for real-time concentration monitoring in practical applications.