In order to explore the erosive wear mechanism of gas-solid two-phase flow carrying sand in natural gas pipelines at the pipe contraction and expansion section, a Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) coupling approach was selected to develop a CFD-DEM model in the pipe contraction and expansion sections. This study analyzed the influence of varying particle size, mass flow rates of particles, diameter ratios of the pipe contraction and expansion sections, and flow velocities of the continuous phase on the erosive wear at the contraction and expansion section within the pipe. The research results reveal a direct relationship between particle size and the maximum wear depth, with a 1.2 mm particle size exhibiting a maximum wear depth 1.7 times greater than that of a 0.4 mm particle. The maximum wear depth increases linearly with the mass flow rate and flow velocity of particles. As the diameter ratio of the contraction section increases, the maximum wear depth initially decreases before it starts to rise again. The maximum wear depth is subject to varying degrees of increase or decrease as influenced by the aforementioned factors. The order of impact of maximum wear depth from high to low is: continuous phase flow velocity>pipe diameter ratio>particle size>particle mass flow rate. The simulation results in this paper can provide valuable insights for the optimization of the design for pipe contraction and expansion section, thereby mitigating the risk of pipeline leak caused by wear during natural gas transportation.