The invention provides a bandwidth distribution method for a coexisting of different transmission rate. The method includes the following steps: an type list table is formed in an OLT for recording the types of different transmission rates ONU; the OLT carries out an unified time-slot distribution to the different rates ONU according to the table to form a uplink bandwidth distribution table; andaccording to the uplink bandwidth distribution table, the bandwidth distribution instruction with different transmission rates are borne by a downlink light channel with different wavelengths. The invention also provides the bandwidth distribution device used for the coexisting of different rates PON.