As one of the most advanced optical detection techniques, photoacoustic spectroscopy has been successfully used in the area of trace gas detection. Realizing a multi-gas photoacoustic spectroscopy sensor while keeping a high detection sensitivity was the design purpose. For the detection application, a multi-gas photoacoustic spectroscopy sensor based on the Helmholtz resonance was designed and optimized. The sensor was modeled by using the finite element method and optimized for its parameters, including the dimensions of excitation cavity, connecting tube and detection cavity. Also the temperature and pressure properties of the sensor were investigated. As a result, the detection sensitivity could be improved by optimizing the parameters and controlling the temperature and pressure. The optimizing result shows that the gas sensor has a best performance with the infrared light source IR-19, and parameters with excitation cavity of Φ38 mm×9 mm, connecting tube of Φ5.9 mm×10.2 mm and detection cavity of Φ30 mm×5.8 mm. Tested by the experiment, the detection limit of 5.08 ppm is achieved for the CO gas detection. The study results also provide the reference for design of photoacoustic sensor in multi-gas detection.