The invention discloses a method and a device for analyzing the newly added capacity of a transmission channel between regional power grids. The method includes the following steps: calculating the capacity scale of a future transmission channel according to the interconnection relationship of multiple regional power grids and the capacity of an existing transmission channel, and establishing an objective function with the minimum capacity scale of the future transmission channel as an optimization objective; establishing a power balance equation according to the interconnection relationship of multiple regional power grids and the existing transmission channel; establishing conventional unit output constraints and energy storage equipment and demand response constraints; and optimizing the objective function according to the power balance equation, the conventional unit output constraints and the energy storage equipment and demand response constraints to generate a power planning model, and analyzing the newly added capacity of a transmission channel between regional power grids by solving the power planning model. The method can guarantee the power balance and the economy of construction of a regional interconnected power system by considering the renewable energy and the load fluctuation and coordinating and considering the planning model of the energy storage and demand response technology.