This paper presents a methodology to solve the Long-term hydrothermal operation planning problem. This methodology is based on the sequential two-stage Dual Dynamic Programming (DDP). The two-stage proposed method uses the Benders' decomposition approach presenting a reduced number of cuts thus resulting in a fast convergence process. The Brazilian power system will be used as a study case to show the efficiency of the proposed method. Also, the results will be compared with the solution obtained in the deterministic approach with the multistage deterministic dual programming considering an average natural energy inflow.