The invention discloses a method and a device for transmitting multicast method, wherein the method comprises the following steps: determining a multicast virtual switching instance (VSI) corresponding to user information according to the user information carried in joint requests after receiving the joint requests sent by a user; determining user information of all joint requests managed by the multicast VSI according to a transmission list, and transmitting the multicast data from the multicast VSI to all users required to joint according to the information of the users required to joint, wherein the transmission list is used for recording a corresponding relation of the multicast VSI and the information of all users required to joint. The invention achieves the purposes of saving network bandwidth and reducing the quantity of protocol messages.