Based on the photoacoustic spectroscopy technology, this paper constructed a simulation model of the H-type differential photoacoustic cell by finite element simulation, and the geometric parameters of the cell were optimized. In addition, the robustness to noise was guaranteed, and the sound pressure and quality factor were greatly increased. The paper chose NO₂ as the target gas to verify the performance of the photoacoustic cell, and a low-cost 450 nm laser diode was used as the excitation light source to match the strong absorption line of NO₂ and avoid photolysis. The experimental results show that the differential characteristic of the photoacoustic cell is consistent with the simulation results. Within the detection time of 5 s, the linearity between photoacoustic signals and different concentrations of samples reaches 0.999, and the minimum detection limit is 124×10^-12, which meets the online detection requirements of NO₂ in an atmospheric environment.