The torpedo water entry impact has a great effect on its underwater ballistic trajectory. In the paper, by wind tunnel experiments we get the torpedo water entry drag coefficient, amending it with supercavitation continuous factor and local cavity effect factor, and then the torpedo motion equation is established. Finally, the large scale nonlinear finite element software MSC.dytran is used to simulate the initial water entry impact of a Disk-Ogive-Head [1] torpedo. Then the motion parameters in the end of this stage are input into the motion equation as initial input values; finally, two parts of data are combined to get the whole parameters. The model uses cavitation number to determine torpedo’s cavity, supercavitation, partial cavity or full wet navigation stage.