Abstract: The drag reduction characteristic of the underwater projectile natural supercavitation was simulated based on the homogeneous equilibrium multiphase theory through using commercial CFD Code FLUENT6.3. The effects of the cavitation number on the location where the cavity of the underwater projectile is closed to and the variation of the drag coefficient are numerically investigated. The effect of the structure parameters of the underwater projectile on the drag reduction characteristics of natural supercavitations is analyzed. The effects of the cavitator diameter, the aspect ratio and different shapes of the afterbody on the drag reduction characteristics of the underwater projectile natural supercavitation were found. The results of the numerical simulation show that: with the diameters of the cavitator increased, the natural supercavitation formed easily, but the capability of the natural supercavitation decreased to some extent. The natural supercavitation came into being hardly as aspect ratio increased, and almost the same that the drag coefficient of a different aspect ratio model was. The development of the cavity induced by different afterbodies was only affected by its shape. The variations of the natural supercavitation’s shape and that of the drag coefficients of different shapes of afterbodies are almost the same as long as the afterbody are covered all over by the cavity.