The valve core and pipeline of the threeway reversing valve in the mud water shield machine takeover system are susceptible to slurry erosion abrasion.The DPM (Discrete Phase Model) model in the computational fluid dynamics was applied to the spool retracting runner and the equaldiameter elbow.The results show that the degree of erosion abrasion on the pipe wall caused by mud flowing through the equaldiameter elbow is more serious than that caused by mud flowing through the reduced diameter elbow.The boss in the reduced diameter elbow can play an effective turbulence effect and can consume the kinetic energy of the mud fluid,which is advantageous to slow the erosion abrasion of the mud on the outer wall surface of the elbow.When the mud flows through different variable diameter pipe,the degree of erosion abrasion on the pipe wall is different,and the erosion wear rate of the mud from the reduced diameter elbow to the equaldiameter elbow is less than that from the equal diameter elbow to the reduced diameter elbow.