The detection of oil-dissolved gases (such as CO, CH4 and H-2) in transformers on-line is an important technology to predict and judge the operating status of transformers. Microstructure and gas sensing performance of AuMoS2 microspheres synthesized by hydrothermal method were investigated in the present research. The results indicated Au-MoS2 based gas sensor has excellent response to CO, CH4 and H-2 gases with maximum responses of 25.48, 16.75 and 8.48 at 30 ppm in their optimum working temperature (150 degrees C, 150 degrees C, 175 degrees C). In addition, First-principle calculation was carried out to expound the sensing mechanism in detail. The conclusions of this study suggest that Au-MoS2 monolayer exhibits a promising applicable future in sensor detecting of oil-dissolved gases in power transformer.