A new photoacustic spectroscopy technique,called differential photoacoustic spectroscopy is presented in this paper.Using a monochromator and a wavelength beam split,two light beams with identical intensity but different in wavelength are obtained at the same time.This two light beams are focal in two photoacoustic detectors respectively and the output of each detectors is transmitted to a lock in amplifier.Then the output (A B) of the lock in amplifier is transmitted to a X Y recorder.Finally the differential photoacoustic spectroscopy is obtained by scanning the wavelength of monochromator.This differential photoacoustic spectroscopy has both the advantages of photoacoustic spectroscopy with high sensitivity and differential spectroscopy with high resolution.