The wall slip is one of the important factors affecting the quality of gun propellant extrusion molding. To improve the accuracy of numerical simulation of the seven-hole nitroguanidine gun propellant extrusion molding, the wall slip mechanism of nitroguanidine gun propellant dough was studied, the mathematical model of gun propellant flow considering the wall slip correction was established. The finite element method was used to simulate the forming process of seven-hore nitroguanidine gun propellant. The pressure field, the velocity field and the velocity vector distribution at the junction of the segment and the forming section were compared and analyzed at cases whether considering the wall slip. The simulation was validated by the gun propellant extrusion test. Results show that the wall slip reduces the forming pressure of gun propellant and improves the uniformity of gun propellant exit rate, which is beneficial to the forming of gun propellant. The error between the actual size and the simulation size of the gun propellant is less than 2.0% in which, the outer diameter error is 0.59%, and the outer arc error 0.36%, the inner arc error 1.80%, the aperture error 1.67%, and the center aperture error 1.72%. The simulation process is in line with the actual processing.