Abstract: In an optical transmission method and system for performing a bidirectional optical transmission at an identical wavelength between an intra-office transmission circuit and in-house transmission circuits with a single-core optical fiber, the intra-office transmission circuit detects, based on a response failure of the in-house transmission circuits, an in-house transmission circuit corresponding to the response failure, and further detects a failure point by transmitting an optical isolated pulse to the in-house transmission circuit corresponding to the response failure in order to automatically detect a disconnection failure of an optical fiber without connecting a specific measuring device.