Abstract: Experimental and numerical investigations were performed on the CH4/Air mixture premixed flame propagation in a horizontal rectangle tube with a wedge obstacle mounted at the bottom. The multiple-lens, Cranz Schardin high speed video system and pressure transducer etc experimental equipment were adopted to visualize the interaction between the wedge block and flame and to measure the flow parameters. Sequences of high-speed images with high definition showing the process of a flame losing its stability under the action of the wedge obstacle and pressure history on the backside of the obstacle were gained. Based on RANS method and EBU-Arrhenius combustion model, a numerical simulation was carried out to simulate the above complex physical phenomenon. Both experimental and numerical results are in good agreement, which show the inherent mechanism of flame acceleration and its front distortion, as well as the nature of a transition from laminar combustion to turbulence during its propagation.