This article introduces the research and application of digital twin technology in the development of power grids. It relies on the Planning Information System management platform of the State Grid Corporation of China, with the goal of scientifically leading the development of a strong smart grid. It takes the Internet of things, blockchain, big data and other technologies as the support, and integrates massive data such as power, pipe trench corridor, regulatory planning and meteorological data, to build an online platform on which the power grid can be planned, constructed, and operated. At present, the Planning Information System platform is based on digital twin technology, which has integrated 22 sets of professional systems such as infrastructure, dispatching, equipment and marketing, and has access to 334 categories and 56 billion pieces of data such as equipment ledger, operation curve, project data and space resources. Through the above research, we have realized the "digital twin" of "physical power grid" and "online power grid", which supports the high-quality development of power grid business.