Embodiments of the present invention provide a line card, an optical module, and an optical network device. The optical module includes at least one electrical interface and at least one optical interface. The wavelength division multiplexer/demultiplexer includes a first interface and a second interface. The panel is disposed on an edge of the mainboard. The electrical interface is electrically connected to the mainboard. The optical interface faces a direction that is from the edge of the mainboard to an interior of the mainboard and that is parallel to the mainboard, and the optical interface is connected to the first interface. The wavelength division multiplexer/demultiplexer is disposed on the mainboard, the second interface is configured to connect to a feeder fiber, and the feeder fiber is configured to connect an optical network device at a sending end and an optical network device at a receiving end.