In order to deal with the challenges brought by the high penetration of renewable energy to the operation and scheduling of a power system, a quantitative evaluation method of flexibility considering wind spillage and load curtailment is proposed. Based on day-ahead and real-time dispatching frameworks, a two-stage robust optimization model with multi-period coupling constraints is established. In the day-ahead dispatching, a security-constrained unit commitment model is established based on wind and load forecasting data. In real-time dispatching, the maximum accommodation range of wind power is calculated considering the uncertainty of the power system and can be described as the do-not-exceed limit problem. For any wind power realization within the limit, the risk of wind spillage and load curtailment in the real-time dispatching stage can be made acceptable by adjusting the day-ahead scheduling. Based on the solution framework of Benders algorithm, and applying strong duality theory and the big-M method, the intractable min-max-min model is reformulated to a mixed integer linear program. Finally, the effectiveness of the proposed method is verified by an example of the modified IEEE-6 and IEEE-118 bus test system. This work is supported by National Natural Science Foundation of China (No. 51777126).