Display of power grid equipment on map is the basic function of power GIS application. According to the statistics, in most of our provinces, the amount of power grid resource data has reached tens of millions or even hundreds of millions. Therefore, the high performance display of massive power grid resource data on web has become a key problem to be solved in the construction of power GIS system. Aiming at the characteristics of GIS data and application of power grid, this paper presents a dynamic loading and rendering method for GIS data of massive power grid resources for Web. This method controls the amount of loaded data by data display rules and power line data compression, thereby reducing the network transmission and drawing pressure. It loads data according to the viewport bound, establishing request cache and data cache on the client to improve the efficiency of data rendering, and uses HTML5 technology for multi-threaded data analysis device symbols rending. It is proved that this method can significantly improve the fluency, interactivity and flexibility of web client-side displaying for massive power resource GIS data, and has greatly improved the user experience.