The present invention belongs to the field of data communication technology. The method includes receiving light signal from peripheral equipment, copying light signal, feeding the signal to one one-out-of-two selector device and to one intermediate communication equipment for processing and re-copying, and feeding one of re-copied light signal to the one-out-of-two selector device for the one-out-of-two selector device to select one of the light signal based on the work state of the intermediate communication equipment and to emit to the equipment in the other party. The flow rate protecting device includes two light splitters for copying light signal and one light switch as the one-out-of-two selector. The present invention is not dependent on the network topologic structure and can realize flow rate protection reliably and may be used in data communication equipment sensitive to interruption.