To elucidate the flow regime characteristics and boundary conditions of gas-solid two-phase flow in horizontal pipe pneumatic conveying, the flow characteristics were studied based on the four-way coupled CFD-DEM method. Based on the experimental verification of flow regimes, the flow characteristics at different superficial gas velocities were analyzed from three perspectives. The results showed that the mean value of the pressure at the inlet and the standard deviation of the pressure fluctuation decreased with the superficial gas velocity, as well as the mass of the standard volume particles. The conveying flow regimes of slug flow, dune flow and stratified flow in the pipe were presented in turn, and the particle distribution in the pipe gradually shifted from filling the entire pipe to the bottom of the pipe. The particle velocity in the middle part of the pipe was the highest for slug flow.