The secure transmission of distributed two-way relay systems is studied. To maximize the secrecy sum rate subject to the aggregate power constraint, an artificial-noise-aided beamforming (ANBF) scheme is proposed. The major difficulty in the ANBF scheme is a non-convex optimization problem. Therefore, a sequential parametric convex approximation (SPCA) algorithm is proposed, together with a New ton iteration method, to optimize the beamforming vector, artificial noise covariance matrix as well as the transmission power in an alternating iterative way. The ANBF scheme is proved to be a generalization of the existing beamforming (BF) scheme without AN and the null space beamforming (NSBF) scheme, and the system design is more universal. Simulation results and performance analysis verify t he efficiency of the proposed ANBF scheme, and reveal that it achieves the highest secrecy sum rate.