Abstract: Using the data obtained from the ground tests based on 2017-T4 aluminum spheres projected by the two-stage light-gas gun impacting 6061-T6 aluminum sheets, and choosing a proper function model, this paper establishes a 3-variable polynomial model with order 2 for the velocity of the front particle of the debris cloud with respect to the sheet thickness, the impact diameter and the impact velocity, making use of the method of the multivariate data fitting. The model is verified by using another group of data and it is shown that the model can give a good forecast for the velocities of the front particle of the debris cloud. The same group of modeling data and a group of test data are also applied to the normalized model. A comparison between the two models shows that the polynomial model is better than the normalized one distinctly regardless of whether the mean squares error or the mean relative error is used. The model can be used to forecast the velocities of the front element of the debris cloud produced by the impact between the space debris and the spacecraft, and be used in the design to protect the spacecraft against the space debris.