Abstract: Dissolved gas-in-oil online monitoring is one of the important means to implement condition-based maintenance for power transformer. Laser Raman spectroscopy（LRS） can directly perform non-contact measurement to mixed gas by a laser with single frequency, especially being suitable for online monitoring. Using LRS to analyze dissolved gas in transformer oil can overcome the disadvantages of traditional online monitoring methods. In this paper, the application of LRS in the dissolved gas-in-oil analysis（DGA） was studied. The Raman characteristic spectra of seven major fault characteristic gases（H2, CH4, C2H6, C2H4, C2H2, CO, CO2） were analyzed, and the qualitative and quantitative analysis methods for the seven characteristic gases based on the characteristic spectra and the least squares method were elaborated. Laser Raman spectroscopy gas detection test platform was built using confocal Raman technology and gas sample cell made by silver plated quartz glass tube. Utilizing this platform, the Raman spectrometry detection characteristics of the seven fault characteristic gases were studied, and the test results were compared with the results measured by gas chromatography in laboratory. The comparison results show that LRS can quantitatively analyze dissolved gas in transformer oil effectively, which lays the foundation for the online monitoring of dissolved gas in transformer oil with LRS.