The present invention discloses a method for transmitting a frame sequence number and a node B and a serving radio network controller, which method comprises: a node B receiving a protocol data unit from a carrier and de-multiplexing the protocol data unit into media access control data streams; the node B inserting a carrier symbol into a carrier indicator field of an enhanced-dedicated transport channel data frame and generating a frame sequence number for every the enhanced-dedicated transport channel data frame transmitted on the carrier; and the node B transmitting the media access control data streams to a serving radio network controller SRNC by using the enhanced-dedicated transport channel data frame. By virtue of the present invention it achieves that the SRNC is capable of obtaining the information regarding network layer data transmission in dual-carrier situation so as to detect the loss of data frames.