Abstract: Nowadays, the law of penetration into the underground target is one of the key points in the weapon development and high value targets protection. Considering the influence of the steel reinforcement on the projectile's trajectory,a contact algorithm is put forward to describe the contact phenomenon between the penetrator and the steel in the penetration into the RC target. The contact algorithm is based on the equivalent single degree of freedom (SDOF) method, where the penetrator is simplified as a ball and the reinforcement steel is considered as the beam with a fixed-fixed boundary, and the resistance of the steel beam is considered as the contact force exerted on the penetrator. The resistance function presented here is validated by the comparison between the simulations with the code and the commercial software AUTODYN. In general, the contact algorithm is reasonable and effective in the simulation of the interaction between the penetrator and the steel.