Cross-border financial communication is extremely important for the development of modern financial services. The society for worldwide interbank financial telecommunications (SWIFT) is the main provider of cross-border financial communications services. Now, telecommunications message transmission is the main business of SWIFT systems to ensure the transmission of messages. Security, accuracy, and efficiency are important goals of SWIFT system. However, the current SWIFT system based on the concept of central architecture has outstanding security risks, low transmission efficiency, and high cost. This study proposes a BCSWIFT system based on the permissioned blockchain distributed consensus mechanism, which can make SWIFT system be optimized. First, the transmission network of the SWIFT system is divided into the main network layer and the additional network layer. Second, a consensus algorithm based on the double-layer network structure is proposed. Third, the telecommunications message exchange and transmission of the BCSWIFT system are introduced. Fourth, for the sake of business confidentiality of financial business data, the mechanism of message data privacy protection for financial institutions. Fifth, the security of BCSWIFT system. This article takes the optimization of the SWIFT system's message transmission service as an example, explaining the basic mechanism of cross-border financial communications based on the permissioned blockchain, to provide new ideas for ensuring the safety, efficiency, accuracy and low-cost operation of cross-border paymen, and also provide an important reference for large-scale commercial application of blockchain technology.