The principle of photoacoustic spectra detection is introduced in this paper.The methyl parathion detection method based on three time light path is proposed. Three photoacoustic spectroscopy signals produced by the alternation of three light filters are weighted, thus the problem of the cross sensitivity in the conventional single light path measurement is overcome.The three time light photoacoustic spectroscopy model is established.An experiment platform for photoacoustic spectroscopy detection is designed,and the measured data are analyzed and compared.The feasibility and accuracy of the proposed method is confirmed.