A method and an apparatus for spectrum defragmentation, where the method includes: obtaining, by a transmit end, a target data stream; sending the target data stream on one line using a to-be-adjusted frequency band; adjusting, on another line, an occupied frequency band of the target data stream from the to-be-adjusted frequency band to a target frequency band; switching the target data stream to the other line; and transmitting the target data stream using the target frequency band.