The invention discloses a self-excitation multi-wavelength dynamically dispatched optical network unit in passive optical network, belonging to the technical field of optical communication. The optical network unit comprises an uplink data transmitter, a downlink data receiver and a first optical circulator, wherein the output end of the first optical circulator is connected with the downlink data receiver for transmitting downlink data optical signals; the input end of the first optical circulator is connected with the uplink data transmitter for transmitting uplink data optical signals; andthe uplink data transmitter comprises a FP multi-longitudinal mode laser, an adjustable band-pass filter, an optical splitter/coupler and an optical reflection ring. In the invention, multi-wavelength dynamically modulated uplink optical carrier is generated based on the self-excitation working mode of the FP multi-longitudinal mode laser, thereby greatly increasing the uplink transmission bandwidth, flexibly and effectively sharing all uplink wavelength resources, improving the use ratio of the uplink wavelength resource, ensuring simple structure and low cost, according with the requirementof colourless transmission of the optical network unit and meeting the development requirement of dramatically increased uplink access ability for users.