Embodiments of the present invention provide a method and device for controlling transmitted power of an optical network unit, and an optical network unit. The method comprises: obtaining identification information of a passive optical network; obtaining the transmitted power of an optical transmitter of an optical line terminal and a minimum sensitivity of an optical receiver of the optical line terminal according to the identification information of the passive optical network; obtaining the received power of the optical receiver of an optical network unit; calculating line attenuation according to the transmitted power of the optical transmitter of the optical line terminal and the received power of the optical receiver of the optical network unit; and adjusting the transmitted power of an optical transmitter of the optical network unit according to the line attenuation and the minimum sensitivity of the optical receiver of the optical line terminal. By means of the method, device and optical network unit
