In order to assess the damage effect of target under the warhead's explosion more accurately and quickly, the algorithm was deduced which considered the velocity fade of fragment. Firstly judge whether intersect the surrounding-box of target by fragment track was proposed, and then calculate the velocity of fragment which intersecting the surrounding-box was used partially traverse the target surfaceelements, until the fragment hitting the target. A calculation case was given. Finally, the influence of missile distance, missile velocity, target velocity and the fragment's static explosion velocity to the excursion of hitting point is discussed.