Abstract: In this paper, we investigate the secure communication problem in relay aided interference systems. To solve this problem, we propose a physical layer encoding based on the mean square error. Specifically, a wiretap model of relay aided interference systems is built and the problem of maximizing the difference of mean-squared errors between legitimate users and eavesdropper is formulated as an optimal problem. To simplify the calculation process, the non-convex problem is split and converted into three convex sub-optimal problems. After that, an iterated algorithm which jointly solves the optimal encoder matrices of transmitter, relay and receiver is proposed. Experimental results show that the security performances in different scenarios are effectively improved by using the proposed algorithm.