Abstract: ‍ ‍As an innovative 6G technology， an intelligent reflecting surface （IRS） can enhance the energy efficiency and security of future B5G/6G networks. Focusing on the high security risks and high energy consumption of IRS-assisted downlink multiple input single output systems， this study analyzed the impact of transmit beamforming and an IRS phase shift matrix on system security and energy-saving communication. Then， we considered a transmission power minimization problem under secrecy rate constraints. A second-order cone programming algorithm based on successive convex approximation was proposed to iteratively solve this non-convex multivariable coupling problem. In contrast to traditional iterative optimization algorithms， this algorithm simultaneously updated all the optimization variables in each iteration and finally obtained a suboptimal solution to the original problem. The findings from the simulations indicated that compared with the three benchmark schemes （the no-IRS scheme， random phase shift scheme， and SDR iterative optimization scheme）， the algorithm proposed here achieved a lower transmission power while ensuring the confidentiality of legitimate users， which proved the effectiveness of the algorithm and great potential of IRSs in future secure and energy-saving communication systems.