With the development of the smart grids in recent years

a number of micro-grids and renewable energy have been generally integrated into the regional power grids. Consequently

a core function of dispatching system—the state estimation has met a problem of low computational efficiency. In order to increase the computational speed

this paper proposes a fast algorithm of distributed state estimation used to regional power grids. In this algorithm

the fast-decoupled and linear estimation are carried out at the lower and upper level

respectively

which can both improve the computational efficiency. The improvement of efficiency is validated by the case studies executed in the IEEE 118-bus system.