The invention discloses a passive optical network architecture and an inter-ONU communication method based on the architecture, in the architecture, an OLT is connected with a plurality of ODNs, the communication method supports mutual communication between different ONUs under the control of the same CO without passing through the CO, in the communication method, the ONUs generate an uplink data frame containing uplink user data and target ODN address signaling, and the uplink data frame is used for sending the uplink user data and the target ODN address signaling to the OLT. The method comprises the following steps of: receiving uplink data by an OLT (Optical Line Terminal), modulating the uplink data to a pre-allocated subcarrier of a system by adopting a frequency division multiplexing technology based on subcarrier multiplexing, distributing downlink wavelength for the data according to address signaling information in the uplink data after the OLT receives the uplink data, and issuing the downlink wavelength to a target ODN (Optical Distribution Network) connected with the OLT, so that the data transmission of each user is only performed between the OLT and an ONU (Optical Network Unit), and the data transmission efficiency is improved. According to the invention, the CO is only responsible for sending the communication authority control instruction and controlling the downlink communication of the OLT, and does not process the uplink ONU data, thereby reducing the occupation of the storage space of the CO caused by the data between the ONUs under the control of the same CO entering the CO, and enabling the CO to meet the requirements of more cross-CO ONU communication.