A method of rigid plastic finite element analysis including the inertia effect has been developed in order to determine the mechanical behavior of penetration caused by collision of a flying projectile with a target. The analysis is based on the double-nodes method and is treated as an axisymmetric problem. The penetrating process is clarified via a method of node separation, which satisfies the condition that plastic deformation energy extends beyond a threshold value. Experiments on collision of two bodies, a cylindrical projectile of steel and a disc target of plasticine or plumbum, were carried out using a test apparatus with projection of compressed air. The experimental results were compared with the calculated results, and it is shown that the calculated results of the residual speed of the projectile and the final shape of the disc target after penetration are in agreement with the experimental results. It is expected that the calculation time of the developed method is less than that of the conventional elasto-plastic approach.