The combustion characteristics and thermal performance of a premixed H-2/air combustion in the micro combustor with a backward-facing step is studied through experimental tests and numerical simulations. The effects of step length and wall thickness on the flame stability and thermal performance of the micro-combustor are presented and compared. The results show that the outer wall temperature can be improved by the reduction of wall thickness and modified through the relocation of the high temperature zone. With the decrease of the step length, the flame location is reduced in the combustion chamber, while the same location of peak temperature is obtained in the combustors with varied wall thicknesses. The efficiency of the micro thermophotovoltaic (micro-TPV) system with GaSb and InGaAsSb PV cells are calculated and compared. The micro-TPV system with GalnAsSb PV cells and the micro-combustor with step length 5 mm and outer diameter 3.6 mm produced the highest energy output and efficiency. (C) 2019 Elsevier Ltd. All rights reserved.