To study the water entry ballistic trajectory of a torpedo, the wind tunnel experiment has been done based on the similarity principle. Then the drag coefficient of the torpedo is got when it enters the water, which is amended by the introduction of continuous supercavitation factor and local cavity effect factor. The vertical plane motion equations are established to get the torpedo's trajectory. The large scale nonlinear transient finite element commercial software MSC. dytran is also used to simulate the initial water entry impact of the Disk-Ogive-Head [1] torpedo, including four special high-speed water entry attitude angles. Then the kinematics parameters as the tail of torpedo submerges in water are input into the motion equation as the initial conditions. Finally, two parts of the data are combined to get the whole kinematic and kinetic parameters. During the calculation, the ballistic modeling uses the cavitation number to determine the torpedo's moving status: in the supercavitation stage, in partial cavity stage or in full wet navigation stage. The simulation results will do reference use to the following trajectory design. In addition, the water impact load and over load calculation of high-speed oblique water entry impact will help to design the intensity of torpedo's shell.