A light transmission assembly includes a light circuit board and a light transmission module. The board is embedded with waveguide layers, the waveguides layers includes core wires and shielding lays sandwiching the core wires, the waveguide layers defines a second light port portion of which the core wires defines vertical end faces. The light transmission module includes a base and a first light port portion projecting from a first face of the base, the first light port portion defines vertical end faces, the base defines a slanting surface at a second face opposite to the first face thereof. The first and second light port portions are aligned with each other when the light transmission module is coupled with light circuit board so that light lines go directly from the core wires through the light transmission module and reflect at the slant surface.