Projectile penetration is always a hot research topic, and the prediction of the penetration depth of the rock targets is mainly depended on the empirical equations. The common empirical formulas are summation of the knowledge of the old bombs or the general aviation bombs, they are not suitable for the new development of the earth penetrator weapons, the calculated results of some formulas are far from the actual results, and the empirical formulas, indeed, are necessarily modified. The similarity theory and the dimensional analysis method are used to determine the key parameters affecting penetration depth, and the function relation is established. Then the empirical formula of the earth penetrator weapons penetrating rock targets is fitted through a large number of data. Numerical simulation is carried out on the earth penetrator weapons penetrating rock targets by ANSYS/LS-DYNA. Compared with the results of the fitting formula and the common empirical formulas, the result indicates that the results of the numerical simulation are well consonant with the results of the fitting formula, and the fitting formula can be applied for predicting the depth of earth penetrator weapons penetrating rock targets.