Quartz-enhanced photoacoustic spectroscopy (QEPAS) is a gas detection technology that has developed rapidly in recent years. It has the advantages of high sensitivity, small equipment size, and immunity to environmental noise. We design an all-solid-state mid-infrared fiber-coupled QEPAS photoacoustic detection module. Under theories of gas thermodynamics and one-dimensional acoustic resonator, the sound pressure distribution and level of the detection module are simulated using COMSOL software. An optomechatronic detection module is then designed and processed. It integrates the acoustic resonator, photoacoustic cell, optical fiber module, and pre-amplification module for easy collimation, high stability, and strong anti-interference ability. With a high-power mid-infrared DFB laser at a central wavelength of 2 μm as the light source, CO₂ detection is carried out via wavelength modulation technology. As a result, a detection limit of 3.7×10 ^-5 is obtained at an integration time of 1 s. Allan variance analysis shows that when the integration time is 1123 s, the detection limit of the system can reach 1.34×10 ^-6. The QEPAS system built on this module can be used to conduct real-time monitoring of indoor CO₂ concentration.