Abstract: Aiming at the explosion propagation process of methane/air mixtures within a confined space, a pipeline model composed of a horizontal pipeline with a closed left-hand side (serving as the ignition end) and an open right-hand side, along with a vertical pipeline, was established. The influence of different positions of the vertical branch pipeline on the methane explosion propagation characteristics was investigated using Fluidyn-MP software. The results indicate that under different positions of the vertical branch pipeline, the vertical branch pipeline reduces the average peak explosion pressure and average peak explosion temperature at each measurement point inside the horizontal pipeline. It increases the peak gas flow velocity at the measurement points located on the left-hand side of the branch opening, while decreasing the peak gas flow velocity at the measurement points on the right-hand side. As the explosion propagation distance increases, the peak pressure at measurement points within the horizontal pipe shows an overall downward trend. The peak explosion pressure at measurement points below the vertical pipe decreases sharply. The peak temperature exhibits a fluctuating downward trend overall, with the peak temperature directly below the vertical pipe decreasing sharply and reaching its minimum value. As the distance between the position of the vertical branch pipeline and the ignition source increases, the reduction in the average peak explosion pressure at each measurement point inside the horizontal pipeline gradually decreases, the peak value of the average explosion temperature fluctuates and decreases, and the average peak gas flow velocity keeps increasing. The average peak explosion pressure at each measurement point inside the vertical pipeline fluctuates and decreases, the average peak explosion temperature gradually decreases, the time-history curve of the gas flow velocity exhibits a multi-peak structure, and the peak gas flow velocity changes from fluctuating increase to fluctuating decrease. Furthermore, when the pressure wave reaches the branch, an expansion fan forms at the corner, causing a sharp increase in gas flow velocity. As the flame front reaches the branch, a pressure-holding surface forms. With the increase of the distance between the vertical branch pipe position and the ignition source, this pressure-holding surface shifts to the right, reducing the pressure relief effect of the vertical pipe.