Embodiments of the present invention provide an optical branching assembly, a passive optical network, and an optical transmission method, which relate to the field of communications and are used to implement a functional diversity of the optical branching assembly. The optical branching assembly includes: a substrate and an optical power distribution area disposed on a surface of the substrate, where the optical power distribution area is coupled to a first optical waveguide, multiple second optical waveguides, and at least one third optical waveguide, and is used to distribute optical power of an optical signal, transmitted through the first optical waveguide, to each of the second optical waveguides and the at least one third optical waveguide; and the third optical waveguide is coupled to the first optical waveguide, where a reflective material is disposed on the third optical waveguide.