How to keep combustion stability and less carbon deposit in micro-channel for the methane wet-air auto-thermal reforming combustion technology is a hot research area all over the world now. Even if there are some literatures with respect to this area, but there are many problems to keep studying. In this paper, the effects on the carbon deposit rule, hydrogen and methane conversion characteristics under lean oxygen at pressure have been studied below 973K by thermodynamic analysis with constant feed gas mass flow. Results show that the carbon deposit increases with increasing the temperature first, and then, it decreases. At the same time, the carbon deposit always decreases with increasing reaction pressure. At the different reaction pressure, the temperature zone of carbon deposit is changed, but the upper temperature limit is around 850K. H2 mass fraction and CH4 conversion ratio are raised with increasing the temperature, decreased with increasing the pressure. Adding pressure helps to reduce carbon deposit and maintain a certain H2 mass fraction and CH4 conversion ratio. All results show the reasonable reaction pressure is 0.2MPa in micro reactor.