In the process of drilling oil and gas Wells, due to the complexity of the formation fluid pressure system and the subjective and objective factors in drilling operations, the original pressure balance in the wellbore may be destroyed, resulting in the formation fluid entering the well and causing the overflow phenomenon. When studying the erosion wear of drilling four-pass, most of them focus on the wear effect caused by two-phase flow, while ignoring the impact caused by gas-liquid-solid three-phase flow. Aiming at the erosion wear problem of four-pass pipeline during the well killing process when gas encroachment occurs, based on the DPM erosion prediction model, FLUENT software is used to numerically simulate the erosion wear rule of four passes when gas encroachment occurs, and the change rule of the erosion wear position and maximum erosion rate of drilling four passes caused by different particle size and flow rate of cuttings is analyzed. The results show that the erosion damage is mainly concentrated in the bypass inlet intersecting line and bypass channel. The gas-liquid-solid three-phase flow caused by gas invasion will aggravate the erosion wear. When the mass flow rate of cuttings is constant, the maximum erosion rate at the intersecting line also increases with the increase of particle size. Only the mass flow rate of cuttings is changed, and the maximum erosion rate increases with the mass flow rate increasing.