When the slurry circulation system of the shield machine is discharged,its slag discharge characteristics directly affect the slag discharge efficiency,and then affect the construction efficiency of the shield machine.In view of the problem that the slag discharge process of the mud pipeline cannot be directly observed in the actual construction,and the movement law of the internal mud and rock slag is not clear,the numerical simulation model of pipeline mud and rock slag coupling was established by using the CFD-DEM coupling method against the background of the three-mode shield subway tunnel construction of Guangzhou Metro Line 7.The influence of key parameters of the slurry circulation system such as slurry flow rate,density,viscosity and pipeline diameter on the slag discharge characteristics of mud pipeline was analyzed through the experimental method of single factor influence.The results show that most of the movement patterns of rock slag particles in the pipeline are moving at the bottom of the pipeline,and the impact on the outside of the bent pipe will be caused when passing through the bent part;the flow rate of the slurry increases at the inner bend as it passes through the bend;with the increase of slurry flow rate,slurry viscosity and decrease of pipeline diameter,the slurry pressure loss increases in the form of quadratic,and the slurry pressure loss increases linearly with the increase of slurry density.