With the large-scale integration of renewable energy

the original operation mode of power system is changed by the temporal and spatial distribution characteristics and uncertainty

thus it becomes increasingly unadaptable for the traditional grid planning to meet the current needs of the power system under the impact of multiple uncertainties. The flexibility index suits to quantify the ability of power system to deal with the uncertainty at different time scales to eliminate or reduce its negative effect

which is of great significance to the security and stability of power system. Combined with generator-grid coordination

the evaluation index of power system flexibility is proposed based on the coordination of supply and demand and comprehensively evaluates the endurance capacity of power system to the uncertainty factors. On the basis of the flexibility index

a bi-level programming model of transmission grid is put forward based on the flexibility and the improved chaos crossover and the mutation genetic algorithm is adopted to obtain the optimal plan. Meanwhile

the simulation of Garver-18 node system demonstrates the effectiveness and feasibility of the proposed indexes and programming model.