Abstract: In order to compare dual-cavity combustor with single-cavity combustor on enhancing the combustion,high-speed photography was employed to investigate hydrogen flame structure when fuel equivalence ratio is 0.07 in scramjet.The results show that,hydrogen flame is stable under small fuel equivalence ratio;the combustion region of upstream-cavity near the orifice is a triangular zone formed by the cavity and its shear layer,and another stable zone is beside the downstream wall,while there is no obvious flame around the injection exit;under the same incoming situation,the wall pressure of single cavity combustor is lower than that of combustors with cavities in parallel and cavities in tandem;and the recirculation zone with slow velocity and high pressure between cavities in tandem is good for the process of combustion;for cavities in tandem,the nearer the cavities' distance is,the higher the wall pressure and more concentrated the heat released from combustion is.