Making full use of the regulating role of flexible resources can optimize the available transfer capability (ATC) of the power grid and improve the safety and economy of system operation. A two-stage stochastic dynamic ATC optimization method considering multiple regulating resources of source-load-storage is proposed. First, dynamic scenario analysis is used to model the uncertainty of new energy output, and an incentive-based demand response model and an energy storage equivalent cycle life cost model based on depth of discharge are established. Secondly, in the first stage, a two-stage stochastic optimization economic dispatch model of source-load-storage is constructed, and the optimization result is used as the base state to establish a day-ahead stochastic dynamic ATC calculation model to determine the congestion period. Then, in the second stage, a day-ahead stochastic dynamic ATC bi-level optimization model is constructed, with the objectives of maximizing the ATC during the congestion period at the upper level and minimizing the base operating cost at the lower level. The interaction between the storage and load response conditions at the upper level and the base unit output conditions at the lower level is determined, and the lower-level model is transformed using Karush-Kuhn-Tucker (KKT) conditions to achieve the analysis of the bi-level model. Finally, the case study indicates that optimizing the operational mode of source-load-storage can not only enhance the ATC but also considers the economic efficiency of system operation.