Composite solid propellant contains more solid particles， so it is difficult to accurately simulate the extrusion process of the propellant in twin-screw extruder with traditional finite element analysis method. Whereas， the coupling of discrete element method （DEM） and computational fluid dynamics （CFD） is an effective method for simulation the production process of composite solid propellant， but it is very difficult to implement. In this paper， based on the calibrated contact model parameters， the simulation of solid particles in solid propellant with aluminum powder and ammonium perchlorate as main components in twin-screw extrusion process was realized with DEM， and then the DEM-CFD coupling calculation of the solid propellant solid particles and the liquid phase was realized. The results show that the transportation of solid propellant particles in twin-screw calculated by DEM is consistent with the experimental law. Comparing the results between DEM-CFD coupled simulation and DEM for solid particles， it can be seen that the fluidity of materials was significantly improved by adding the liquid phase The filling rate of materials in the screw conveying section increases from 20% to 40%， and the average conveying speed of solid particles increases by 150%， but the stress of screw does not change much.