Abstract: The uncertainty of wind power output brings great challenges to the planning and optimal operation of power system.The flexibility reformation of thermal power units can effectively improve the peak regulation capacity of the power system and promote the accommodation of wind power. The uncertain wind power output is modeled by box constraint and 1-norm constraint.By considering the technical advantages and economic cost of the flexibility reformation of thermal power units, from the perspective of the overall value of the power system, and based on the light robust optimization theory, a generation expansion planning model with the minimum sum of investment cost and system operation cost is established. The proposed model improves the conservative degree of the traditional robust planning model and improves the economy of the planning scheme. The improved model is analyzed in the improved IEEE-RTS24 node system and an actual system of a regional power grid. Results of the example verify the robustness and economy of the proposed model.