Energy conversion efficiency of a micro thermophotovoltaic (TPV) system strongly depends on wall temperature of micro combustors and its uniformity. In this work, a 3D numerical model is built to investigate effects of inlet pressure on premixed H-2/air combustion in a micro-cylindrical combustor with a step. The variation of velocity, temperature and specific entropy field are analyzed. Moreover, in order to characterize the uniformity of wall temperature, a nonuniformity coefficient R-T,R-w is introduced. Results suggest that the variation of velocity, temperature and specific entropy field is mainly existed at the reaction and outlet regions. And the highest mean wall temperature (1265.59 K) is arrived at p(in) = 0 MPa, while the lowest nonuniformity coefficient R-T,R-w (5.06) and the highest exergy efficiency (40.29%) is approached at p(in) = 0.1 MPa. In the viewpoint of energy usage, the micro combustion system has the best performance at p(in) = 0.1 MPa due to that it has the potentiality to obtain better energy conversion efficiency and higher exergy efficiency. This work provides us a direction to improve the performance of the micro combustor without changing the structure of the micro combustor, and can combine with other optimization methods. (C) 2016 Elsevier Ltd. All rights reserved.