In order to solve the problem that complex aerodynamic interferences which exist in missile separating from cavity effects missile' s initial trajectory and auto-control terminal point scatter. Computational fluid dynamic (CFD) method coupled with 6 degree-of-freedom equations was established. Aircraft with missile computational model and trajectory program was developed. The missile motion was captured accurately through the dynamic mesh technology. Parameters such as force, displacement and attitude were got and passed as inputs of missile auto-control trajectory program and the scatter of auto-control terminal point was computed. The simulation results indicated the great influence on the initial trajectory parameters and on the longitudinal and lateral scatter of auto-control terminal point. The method can deal with pneumatic tight coupled with kinematic problems of missile.