The embodiments of the present invention relate to the field of communications and provide a path selection method, optical network controller and optical transmission network, for addressing a problem in prior art in which a physical path transmitting the optical signal cannot correctly transmit the optical signal and uses an excessive number of relay boards. The method comprises: taking any OTU as a source node and any other OTU as a destination node, acquiring a physical path between the source node and the destination node; in the physical path, determining a directly reachable path and a path reachable by relay; if there exists a directly reachable path between a transmitting end OTU and a receiving end OTU, in which the transmitting end OTU is taken as the source node and the receiving end OTU is taken as the destination node, then selecting the directly reachable path to transmit the optical signal, otherwise, selecting the path reachable by relay to transmit the optical signal, in which the transmitting end OTU is taken as the source node and the receiving end OTU is taken as the destination node. The embodiments of the present invention are used to select a path of the optical signal.