A multimedia data transmission method, comprising: a first transmission device located in a first network obtaining a multimedia file descriptor and a multimedia file to be transmitted which have a correspondence, wherein the multimedia file descriptor and the multimedia file are stored in different memories, and wherein, the first transmission device obtains the multimedia file descriptor from the head of the transmission queue provided in the first transmission device; and the first transmission device obtains the multimedia file from a device in which the multimedia file is stored, which device is indicated by the multimedia file address in the obtained multimedia file descriptor; the first transmission device encoding content of the multimedia file descriptor and content of the multimedia file into a multimedia transmission file in a first format according to a predetermined rule; the first transmission device sending the multimedia transmission file to a second transmission device located in a second network; characterized in that, in addition to the first transmission device and the second transmission device, the predetermined rule and the first format is known to the first transmission device and the second transmission device, but unknown to a third party; and wherein after the first transmission device sends the multimedia transmission file to the second transmission device located in the second network, the method further comprises: if the first transmission device does not receive a response message sent by the second transmission device within a predetermined time period indicating successful reception of the multimedia transmission file, or if the first transmission device receives a response message sent by the second transmission device within a predetermined time period indicating failure in receiving the multimedia transmission file, then the first transmission device inserting the multimedia file descriptor to the end of a transmission queue. a first transmission device located in a first network obtaining a multimedia file descriptor and a multimedia file to be transmitted which have a correspondence, wherein the multimedia file descriptor and the multimedia file are stored in different memories, and wherein, the first transmission device obtains the multimedia file descriptor from the head of the transmission queue provided in the first transmission device; and the first transmission device obtains the multimedia file from a device in which the multimedia file is stored, which device is indicated by the multimedia file address in the obtained multimedia file descriptor; the first transmission device encoding content of the multimedia file descriptor and content of the multimedia file into a multimedia transmission file in a first format according to a predetermined rule; the first transmission device sending the multimedia transmission file to a second transmission device located in a second network; characterized in that, in addition to the first transmission device and the second transmission device, the predetermined rule and the first format is known to the first transmission device and the second transmission device, but unknown to a third party; and wherein after the first transmission device sends the multimedia transmission file to the second transmission device located in the second network, the method further comprises: if the first transmission device does not receive a response message sent by the second transmission device within a predetermined time period indicating successful reception of the multimedia transmission file, or if the first transmission device receives a response message sent by the second transmission device within a predetermined time period indicating failure in receiving the multimedia transmission file, then the first transmission device inserting the multimedia file descriptor to the end of a transmission queue.