We investigate the impact of the initial separation velocity on the trajectory and aerodynamics of the missile and booster during cold separation. A numerical simulation method that couples unsteady computational fluid dynamics with a six degree-of-freedom solver is adopted. The paper analysis the separation processes between the missile and booster under various initial separation velocities. Simulation results reveal two distinct flow structures during the separation process： one characterized by recirculation and the other characterized by wake interaction. The paper analyzes the relationship between these typical flow structures and aerodynamics. A fitting curve tailored to the separation problem is established to predict the trajectory. In addition， the paper analyzes the pitching characteristics of the missile. The analysis in this paper provides a theoretical basis for the design of separation strategies. The fitting curve established in this paper provides a rapid prediction method for trajectory design.