In order to solve the problem that correspondences are easy to be lost or tampered with, and there are great security risks in the process of circulation, a digital platform for correspondences based on blockchain technology is designed. The three-layer architecture of the platform is designed through the platform basic layer, the business layer and the application management layer. Under the platform architecture, the entity relationship and the database table are confirmed, and the platform database design is completed. The platform business units are designed based on the blockchain technology: the electronic correspondence generation unit, the correspondence classification and filing unit, the correspondence block storage unit, and the platform security protection unit. The application test of the platform shows that the overlap coefficient and safety index of the platform based on blockchain technology reach the relative maximum, which proves the functionality of the platform.