The real-time database is one of the cores of the energy management system（EMS）， on which is based most of the real-time data processing. Introducing the index will greatly optimize the real-time database searching operation to improve its performance. The searching algorithm is described alongside the realization of the HASH index， the HASH index with double overflow areas for“parent-child” type searching is designed and its data structure and search algorithm are treated. It is shown that the HASH index with double overflow areas is a suitable index for“parent-child” type searching with high search efficiency.