The invention discloses a subcarrier multicasting transmission system in a wavelength division multiplexing passive optical network, which comprises an optical line terminal, two feed-in line optical fibers, a remote node, a plurality of distribution line optical fibers and a plurality of optical network units. The remote node comprises a second arrayed waveguide grating and a third arrayed waveguide grating, wherein the optical line terminal is connected to the input port of the second arrayed waveguide grating of the remote node through the first feed-in line optical fiber, the output port of the second arrayed waveguide grating is connected to the input port of the optical network unit of a corresponding wavelength channel, the output port of the optical network unit is connected to the corresponding input port of the third arrayed waveguide grating of the remote node, and the output port of the third arrayed waveguide grating is connected to the optical line terminal through the second feed-in line optical fiber. As the output of a switch-controlled multicasting subcarrier emitter, the invention realizes dynamic and rapidly-adjustable multicasting services, omits the liquid source required by the uplink transmission, lowers the power and saves the cost.