In view of the effects of the vertical deflection on trajectory impact accuracy, the influence mechanisms of the vertical deflection on the launching coordinate system, the initial parameter, the force during the flight, the control criteria of the program angle, and the trajectory parameter under the geocentric coordinate system were analyzed respectively by combining with the particle dynamics model of the ballistic vehicle. Then, the mathematical models of the effects of the vertical deflection were established. Furthermore, based on the given computing method of trajectory impact deflection and taking a flight trajectory as example, the impact errors under different geodetic latitude of launch point and different launch azimuth angle were presented quantitatively. The research is of great reference value in the aspect of the improvement of the impact accuracy for the ballistic vehicle.