The wide-area security defense system (WASDS) platform of Guizhou Power Grid (GZPG) in China was developed based on the wide-area measurement system (WAMS), which is composed of master-station located at the dispatching center of GZPG and twenty two sub-stations installed in power plants and 500kV substations. This paper describes the implementation of the software platform which consists of three parts: data sharing service, calculation engine and visualization module. The paper focuses on the design of the data sharing service, the calculation engine of low frequency oscillation monitoring system (LOMS) which is the key part of the platform and the visualization module. This platform has been running in the dispatching centre of GZPG. Tests on measured data recorded by WAMS are presented which illustrate the benefits of the platform and show an excellent performance.