Abstract: This article presents the effect of suddenly extended cross-sectional area of horizontal pipe on the methane explosion shock wave propagation characteristics. In the experiment, the expansion pipe is arranged at different locations of the horizontal pipe, and the flame propagation speed, the explosion pressure and the explosion pressure rising rate over the expansion pipe has been determined to reveal the effect of suddenly extended cross-sectional area of horizontal pipe on the methane explosion shock wave propagation. The results show that the transmission of shock wave from the explosion is greatly affected by the suddenly extended cross-sectional area of horizontal pipe because the extending of the cross-sectional area of horizontal pipe results in the apparent gas expansion that leads to the obvious attenuation of shock wave explosion overpressure.