Abstract: Differential cryptanalysis of key recovery has long been plagued by cumbersome processes and a high risk of errors. To improve the efficiency of key recovery, an improved automated key recovery method for SPN block ciphers based on differential cryptanalysis is proposed. This method constructs a directed graph model based on the differential constraints and dependencies of active S-boxes in the extended rounds, transforming the key recovery problem into a node partitioning and optimal processing order problem. By utilizing a filtering mechanism and a dynamic subgraph merging strategy, the method reduces the complexity of key recovery and directly generates the optimal key recovery order. To address the complex issue of key relationship expression generation, a universal algorithm for the automated generation of key relationship expressions for the highest recovery round is introduced. Through a formal analysis of the key generation process, the algorithm automatically and accurately derives the mutual dependencies between the keys of each round. Additionally, a hierarchical filtering mechanism is employed to effectively filter out key bits that did not participate in the encryption process, avoiding redundant guesses and significantly reducing the key recovery search space. The proposed method is applied to the related key recovery of 26-round GIFT-64, as well as the single-key recovery of 18-round RECTANGLE-80 and PRESENT-80. The results demonstrate that the method efficiently generates the optimal key recovery order, with time complexities of 2^115.96, 2^69.83, and 2^59, respectively.