Based on the impact of extreme weather on power system operation planning, this paper constructs a scenario library that contains a variety of extreme weather types, and transforms flexibility into probability constraints into long-term planning models. The research focused on the complex characteristics of source-network-charge-storage cooperative operation, and proposed a long-term flexible operation planning method. The method comprehensively considered the effects of extreme weather such as high temperature, low temperature, rainstorm, drought, and the like on the power generation, transmission, distribution, and load of the power system, and generated a representative extreme weather scene sequence by utilizing techniques such as Monte-Carlo simulation and Latin-Hypercube-Sampler, and then constructed a scene library. On this basis, the flexibility abundance index system was quantitative, and the flexibility abundance level of the system under different scenarios was evaluated. Then, it was transformed into a probability constraint form, and a long-term operation planning model of multi-objective optimization was constructed. Mixed integral linear programming, genetic algorithm, and other solving algorithms were used to solve it. The results show that the proposed method can significantly enhance the adaptability and reliability of the power system to extreme weather while reducing the operating cost of the system. It provides a new perspective and solution for the long-term planning of the power system, and has important theoretical and practical value.