Power systems are generating masses of data, including measurement and simulation data. To operate and control power systems more effectively, this paper establishes a distributed platform to store, read, and compute massive amounts of data. Our distributed computing platform can support online simulation based power system security knowledge discovery through big data analysis. First, a framework for a distributed computing platform is designed. Then, distributed algorithms are developed, including a distributed massive sampling simulation method and a distributed feature selection method. Next, the software platform and hardware platform for the distributed computing platform are established. Finally, the platform is applied to the Guangdong Province Power System in China to evaluate its accuracy and efficiency. The simulation results show that the distributed computing platform can improve computing efficiency and perform better than a centralized platform.