By combining the wavelength demodulation and second harmonics, the trace H₂S gas is detected based on the quartz-enhanced photoacoustic spectroscopy (QEPAS). A distributed feedback semiconductor laser with an output wavelength of 1578 nm is used as the excitation source. Furthermore, a finite element analysis method is used in the simulation calculation for a quartz tuning fork, typically used in QEPAS systems, to obtain its first six modes and resonance frequencies. In an experiment, an acoustic micro-resonator with a length of 4 mm and an inner diameter of 0.7 mm is added, and a transimpedance amplifying circuit is optimized to detect the H₂S gas under optimal experimental conditions. The results denote that the second harmonic signal of the QEPAS system exhibits a strongly linear relation with the H₂S gas concentration, and a detection limit of 19.3×10 ^-6 is obtained.