Data synchronization method, device and system

The invention discloses a data synchronization method, device and system. The data synchronization method comprises the steps: a user data synchronization proxy server receives a data synchronization request sent by a user terminal logged in the server and then obtains user information carried by the request and user data to be synchronized; the user data synchronization proxy server queries other user terminals bound with the user information and logged in the server according to the obtained user information; the user data synchronization proxy server sends the obtained user data to be synchronized to the queried user terminals, and data synchronization among multiple terminals is achieved by adding a proxy server based on an existing data synchronization system structure.