To improve the reliability of separation mechanism and the safety of the assemble processes, a new type shear separation mechanism is designed, the improved design has the advantage of small-scale explosive and low overload. By engineering calculating, the theory calculation and checking was carried on to the separated explosive quantity and conjunction strength, the separation explosive quantity and the reliability of this separation mechanism were numerical simulated and analyzed by the finite element software LS-DYNA. Comparing with experimental analysis, numerical simulation results were exactly consistent with the experimental results. Experiment and simulation results show that the improved separation mechanism can realize the mission of separation correctly, enhance the conjunction strength of the rocket body at the same time, meet the safety design requirements of the ammunition production.