The invention discloses a data sharing method and device of an interactive whiteboard and a communication system. The method relates to an SDK server, a first client and a second client group. The method comprises the following steps of: firstly, converting a document uploaded by the first client into picture information, and broadcasting the picture information to each client by the SDK server; making each client request a document picture with watermark information according to the picture information, create the same document whiteboard in real time and display the document picture; and meanwhile, making the SDK server broadcast the graffiti operation of a user on the document to other clients, thereby realizing that synchronous display of the operation. According to the method, multi-party document sharing and graffiti synchronous display can be realized, the problems of slow data transmission, long time delay, poor interactive experience and the like during communication of a traditional interactive whiteboard are solved, the problems of tampering, picture stealing and the like are effectively prevented by adding character watermarks to document pictures, the requirements of document sharing in the fields of finance, education and the like are met, and more convenient, safer and more efficient interaction experience is brought.