A new gas detector based on a novel photoacoustic scheme named Differential Mode Excitation Photoacoustic Spectroscopy (DME-PAS) is presented. This method takes advantage of the selective excitation of two different modes in a resonant photoacoustic cell and the gas concentration is derived from the amplitude ratio of these acoustic modes indirectly. The method can detect different gas with optical filter. Efficient data processing cell DSP was chosen as central cell, reducing the system components and making faster a reaction. Meanwhile, it’s convenient to change detecting algorithm according to modifying program. Experiments show that the obtained limit of detection is 23 ppm·m-1 at 98 000Pa and 295 K.