A method for backing up data of a storage system, where at least two mirroring channels are provided between a first mainboard and a second mainboard of a storage system, and the method includes: transmitting data through at least one effective mirroring channel if all the mirroring channels are effective; and transmitting the data through remaining mirroring channel(s) if at least one of the mirroring channels for transmitting the data fails. The method enables traffic to be transmitted evenly on normal mirroring channels, and ensures maximized utilization of the bandwidth of mirroring channels.