To better reveal the characteristics of the power grid with its complexity and identify the key parts that may trigger a large-scale accident within the grid

the existing power grid complex network model is improved by the definition of power transmission path

weighted power transmission distance and path transmission capability

which now complies with the basic electrical law of power grid and the physical constraints. Based on the improved power grid complex network model

an evaluation index set of the key bus and branches within the grid is established

including indices of distance degree

capability degree

hub betweenness

distance betweenness and capability betweenness

which fully considers the variety of tasks that each and every key bus and key branch undertake in the grid structure and operation. Simulations of both IEEE typical test system and Hubei power grid are conducted using the proposed model and algorithm

with key parts identification yielding good results. In comparison with some existing methods

the rationality and effectiveness of the proposed algorithm are verified.