The direction and positioning of the missile could be affected by the vertical deflection which is at the launch point, so the impact point errors will increase. Based on the launch coordination, the target point position deviation formula which is caused by vertical deflection is deduced in this paper. The correction precise of the vertical deflection is also a factor of the impact point error. The simulation based on the deviation formula is conducted to analyze the affection of the vertical deflection and the correction precise of the vertical deflection. And the results show that the vertical deflection can lead to 1km error for the long range missile. In addition, if the precision of vertical deflection were improved , the impact point errors will be reduced 85m.