[Objectives] Numerical simulation is used to study the anti-penetration performance and energy absorption mode of the stiffened plate, as well as the influence of different stiffened bars on the flight attitude of the projectile body.[Methods] The finite element software LS-DYNA is used to simulate the process of the truncated oval-nosed projectile penetrating the stiffened plate, and the results of the numerical simulation are compared with the experiment to verify the reliability of the numerical simulation method. Momentum method and mass equivalent method are used to forecast the residual velocity of the projectile respectively, and the applicability of different theoretical methods in different velocity ranges is compared. Besides, the deformation energy of different regions of the stiffened plate is extracted to analyze the influence of the initial velocity of the projectile body on the energy absorption mode of the target plate. Finally, the structure of the stiffeners is changed and the influence of the relative position of the stiffeners on the penetration attitude of the projectile body is analyzed. [Results] The results show that the mass equivalence method is more accurate than the momentum method in predicting the residual velocity of the stiffened plate when the initial velocity of the projectile body is in the range of 300-900m/s. The ratio of the deformation energy of the stiffened plate to the energy loss of the projectile body decreases with the increase of the initial velocity of the projectile body. The effect of T - stiffened plate on trajectory is greater than that of rectangular - stiffened plate. [Conclusions] The related calculation method and the research results have certain reference value for the research and engineering application on the anti-penetration of stiffened plate.