Abstract: The aerodynamic characteristics of the grid fin are studied by employing CFD approach based on structured/unstructured hybrid mesh technique. The computational method is validated by the wind tunnel measurements to attain engineering accuracy. The research on one single grid fin indicates that, in the case of transonic choking, the coming subsonic airstream forward of the grid fin goes around its outer edge to achieve the mass flux adjusting, while in the case of supersonic choking, the coming supersonic flow is decreased to subsonic by the web-shaped detached shock waves produced by the grid fin and then the mass flux is adjusted, the computed results are in agreement with the range of upper and lower critical Mach numbers predicted by the theoretical estimations. The computational results show that, once the transonic flow past the grid fin presents choking phenomenon, the choking has a self-adjusting effect, which sustains a similar flow in the flow passage of the grid fin through outflowing and then preserve the aerodynamic characteristics essentrially steady; and for the decrease of mass flux, the lift efficiency drops and the static stability of the missile also decreases.