Ensure system reliability and economy. Aiming at the characteristics of power grids such as UHVDC access, distributed new energy penetration, and differentiated load characteristics in the existing power grid, a method for optimizing the configuration of the reserve capacity between subareas of a regional power considering reliability is proposed. Based on the constraints of frequency regulation performance requirements under the accident conditions of each subarea and the grid regulation requirements under non-accident conditions and reliability index of subarea this optimal configuration model for subarea reserve capacity is established with the minimum total reserve capacity of the entire power grid as the optimization objective. Considering the mathematical characteristics of the model, a solution method of ‘linear programming and iterative optimization’ is proposed. This method is conducive to reducing the total reserve capacity of the system and improving the overall operation reliability and economy of the power grid on the basis of guaranteeing the regulation and control performance and reliability requirements of each subarea of the power grid.