Chromatographic columns and gas sensors used in online monitoring devices of dissolved gases in transformer oil have some disadvantages such as the consumption of carrier gas and the failure of long stability. Photoacoustic spectrometry（PAS） is a highly sensitive gas analyzing method without the shortcoming of gas consumption， thus overcoming the disadvantages of the previous online monitoring methods. An investigation is made on the application of PAS in analyzing dissolved gases in transformer oil and a device based on PAS has been designed for the gas-in-oil analysis. The infrared characteristic spectra of CH4 ， C2 H6 ， C2 H4 ， C2 H2 ， CO and CO2are given and the weighted least square method is adopted for the quantitative analysis of CH4 ， C2 H6 ， C2 H4 ， C2 H2 ， CO and CO2in the mixture consisting of two gases. The analysis results are compared with the actual concentrations and those measured by gas chromatography. The comparison results show that PAS is effective in analyzing dissolved gases in transformer oil. Hence fine prospects for its application in on-line monitoring of such gases.