In this paper, we take account of a one-way wireless multi-relay network including one source, one destination and multiple eavesdroppers. To ensure the security for this system, the null space AF (Amplify-and-Forward) relay beamforming design is mentioned in which the aim is to find the optimal beamforming vector to maximize the system secrecy rate while completely eliminating the signal on the eavesdroppers’ channel. The existing methods in the literature for handling such problem are based on a semidefinite relaxation (SDR) technique. We introduce herein a novel approach relied on DC (difference of convex functions) programming and DCA (DC algorithms). We first reformulate the considered problem as a standard DC program, which minimize a DC function constrained by a convex set and then develop a DCA scheme to solve it. The experimental performance shows that the secrecy rates obtained by the DCA based algorithm are better than those achieved by the existing one.