With the expansion of the scale of the urban power grid, there is a gradual change from ring network to grid partition. A new 220kV grid partitioning model based on partitioning load evenness, considering several reality constraints, is established in this paper. In order to reduce the feasible region of the optimization problem, the improved genetic algorithm is adopted, where the feasible operation modes of each channel is prearranged. At last, a case of actual big-city grid is analyzed to illustrate the rightness and validation of the partitioning strategy.