The invention discloses an OFDMA (Orthogonal Frequency Division Multiplex Address)-based mixed passive optical network transmission system comprising an optical line terminal, an array waveguide grating, a feeder optical fiber and a plurality of sub passive optical networks, wherein the sub passive optical networks consist of remote nodes and a plurality of optical network units connected with the remote nodes by distributed optical fibers. By adopting a two-stage access technology and using a fixed wavelength channel, the optical network transmission system has simple structure, is easy to realize, can be updated and reformed on the basis of the traditional passive optical network and meets the requirements of an access network on long distance and wideband; meanwhile, compared with the wavelength division multiplexing passive optical network system structure for adding users by increasing the wavelength, the invention can reduce the cost of the system to a certain degree.