Dynamic security region (DSR) gives system engineers systematic and global information about the feasible operation region in power injection space. This paper is a result of an investigation into the use of DSR concept and its effective application in power systems. It particularly concerns with developing a software-based tool for the dynamic security assessment in the online operation environment. A fast direct method used for computing hyper-plane boundary of the DSR is described. In virtue of being practical of the direct method, a new software package, named Power System Dynamic Security Region (PSDSR) is developed. Following a brief discussion about the main requirements, the paper gives a summary of the development of PSDSR from both the software architecture and the function implementation. A most distinctive character, result visualization, with the related group reduction technology is emphasized.