The flame stability of biogas blended with hydrogen combustion was experimentally studied in the constant volume combustion bomb. The variations of characteristic parameters of flame instability and effect of pressure and fuel component proportion on flame shape were analyzed. The experimental results show that the flame instability increases with the decrease of equivalence ratio, and the global flame stability decreases with increase of CO2 fractions. With increase of initial pressure of biogas and hydrogen mixture, Markstein length decreases, hydrodynamic instability decreases, but the thermal mass diffusion instability has no effect. The effect of increase of the hydrogen ratio on flame stability is more obvious, with the increase of initial pressure and hydrogen ratio together, both hydrodynamic instability and thermal mass diffusion instability increase. This research can provide experimental basis for the design and development of biogas blended with hydrogen engines. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.