Side wall shock wave was introduced in supersonic combustor based on cavity. In order to study the internal flow characteristics of the combustor, nanoparticle planer laser scattering and particle image velocimetry technologies were employed to observe internal flow field of combustor model made by glass. Gray images and average velocity distributions of non-reaction flow field in side view and top view were caught by experimental facilities. Observation results reveal that: speed and density of fluid inside cavity are low in the region far away from the side wall; mass and momentum exchange is enhanced in the region near the side wall on condition of side wall shock wave with high speed and density; boundary layer of combustor bottom wall becomes nonuniform due to side wall shock waves, and large scale of low speed region generates at the rear of cavity with obvious three-dimensional characteristics.