The voltage-grading and district-dividing operation in power systems has become an important measure to limit fault current. A 220 kV power grid optimization model is firstly established to overcome shortcomings of district-dividing by experience or heuristic methods in the paper. The object function for optimal model is maximizing uniform load-rate of the main transformer in each 220 kV zone. The constraint condition includes network loss， supply reliability， fault current limit on 220 kV bus bar and other network constraints . Tabu search algorithm is applied to solve the optimization problem. Finally the method is simulated with a practical example of Jiangsu power grid in 2008 summer peak load data. The simulation result shows the above method is validated.