The technology of this application relates to a user data management method and a related device, to improve user information security. The method in embodiments of this application includes a data request device sends a first request to a blockchain platform, where the first request indicates that the data request device needs to access a data storage device. The data request device receives first permission information sent by the blockchain platform, where the first permission information indicates whether the data request device has permission to access the data storage device. If the first permission information indicates that the data request device has the permission to access the data storage device, the data request device sends a second request to the data storage device, where the second request includes an access address.