Abstract In order to achieve a better energy conversion efficiency, a T-shaped micro-combustor with porous medium and ring-shaped ribs is proposed and studied in this work. For this, 3D model of a premixed H2/air-fuelled combustor is developed with k-e turbulence and EDC chemical reaction models applied. The model is first validated with the experimental data available in the literature and then used to evaluate the effects of (1) the rib, (2) inlet flow velocity of the fuel–air mixture, (3) the axial location, (4) the porosity of porous medium, and (5) its size. The temperature difference is observed to be reduced by 60.73 K than that of conventional I-shaped combustor with the same surface area as the inlet velocity is 5 m/s. In addition, the size and location of porous medium are found to affect temperature distribution. To gain insights on the energy losses and thermodynamic efficiency, entropy generation analysis is conducted. It is revealed that the thermodynamic second law efficiencies of the combustors with porous medium are found to exceed 60%. This study proposed a novel design of a micro-combustor with porous medium implemented for micro-thermophotovoltaic system which can achieve a more uniform outer wall temperature and a higher energy conversion efficiency.