The invention relates to a device for converting a transmission network into an active network, comprising one or a plurality of transmission input interface units for connecting an output end of a transmission line, one or a plurality of transmission output interface units for connecting an input end of the transmission line, an IP network interface unit for connecting a data network, a message processing unit for sorting messages and actively triggering and a poweroff straight-through unit for physically connecting the transmission input interface unit and the corresponding transmission output interface unit into a standard transmission line after powering off; and the transmission line can be converted into the active transmission network by increasing an active network conversion device at the appropriate position of the transmission line, therefore, the business functions of increasing columns in transmitted multimedia (in particular to video) messages as well as altering or canceling fields or instructions in transmitted control messages are provided.