In this paper, a new type of micro combustor is designed to solve the problems of low output performance, insufficient heat source and low quality heat source of combustion-based micro thermoelectric systems. The combustor designed in this paper has the opposite intake arrangement, partial porous medium(PM) filling, central raised cavity and multistage sudden expansion structure. The effects of filling ratio of PM, thermal conductivity of PM and input power (Pin) on the thermal characteristics of combustor were investigated by numerical method. The results show that partially filled PM can stabilize the combustion position and shape, and increase the proportion of available energy of the combustor, so as to provide sufficient heat source for the thermoelectric system. The uniformity of combustor plane temperature increases with the increase of PM filling ratio and thermal conductivity. The combustible range of the combustor is 20–140 W. At the same time, at higher Pin, the filling ratio and thermal conductivity of the PM improve the thermal characteristics more obviously, so as to provide high quality heat source for the thermoelectric system. It is clear that strengthening heat transfer capacity, improving temperature uniformity and improving combustion stability are important ways to improve the thermal characteristics of combustor. In addition, the emission performance of the improvement effect is strong. Therefore, this research can be utilized as effective and feasible guidance for researching thermoelectric system and provide useful insights for the research of system heat source, i.e. combustor. •A new type of micro combustor is designed to improve system performance.•A numerical model is developed to study the characteristics of combustor•Sufficient heat energy and wide combustion range are realized.•Several ways to improve the combustor thermal characteristics are obtained.•The emission performance of micro combustor is improved to some extent.