Embodiments of the present invention disclose a fiber recognition method, an optical line terminal, and a system. The method includes: obtaining, by an optical line terminal, identification information of a fiber connected to an optical line terminal and to be recognized; generating, by the optical line terminal, a data frame that includes the identification information of the fiber to be recognized; transmitting, by the optical line terminal, optical signals that are generated according to the data frame to the fiber to be recognized, so as to make a fiber recognition instrument implement identification for the fiber to be recognized. The present invention can implement fiber recognition easily and conveniently. When a new ONU user is added to a distributed network, service interruption can also be avoided for a user who is normally using a service, and the cost is low.