Scramjet engine is one of the most important components of air-breathing hypersonic vehicles, and the research on flame structures in the combustion chamber of scramjet engines plays a significant role in studying the mechanism of flame stabilization of the supersonic combustion. Two-dimensional distributions of CH were measured at a direct connect test facility using the PLIF (planar laser-induced fluorescence) technique to visualize the flame heat-release structures in a cavity-stabilized scramjet combustor. Verification and optimization of the CH-PLIF technique were conducted in a methane/air premixed lowspeed flame generated by a jet flame burner. Two-dimensional distributions of flame heat-release structures in the scramjet combustor were achieved by using the CH-PLIF technique. OH-PLIF images and CH chemiluminescence images were also performed in the scramjet combustor to compare these images with the CHPLIF images. Experimental results show that the heat-release zones of the low-speed premixed jet flames can become distorted, wrinkled and separated. The heat-release zones are highly wrinkled with the increasing Reynolds numbers. The heat-release zones with a thickness of 0.5~6.5 mm in the cavity-stabilized scramjet combustor become highly distorted and wrinkled, and the separation of the heat-release zones can be observed. It is found that the CH-PLIF technique is able to visualize the heat-release zones in cavity-stabilized scramjet combustors and can play a promising role in understanding cavity stabilization mechanisms of the supersonic combustion.