How to accurately track the flight trajectory of altitude vehicle at unpowered phase is the hot and tough problem in the field of space measurement and control. Based on the analysis of forces acting on the flight vehicle, its rigid movement state equation has been established, and the quality control scheme has also been put forward adopting hierarchical clustering technique to figure out the precise position of impact point. The feasibility and effectiveness of the suggested quality control scheme has been illustrated by simulated example, in which the influence caused by air drag, gravity and iterative step has been researched. The conclusion shows that the flight trajectory of altitude vehicle at unpowered phase could be accurately calculated with offered mathematics model, and the impact point could be automatically estimated.