An optical-electrical conversion module includes a circuit board, a planar optical waveguide formed on the circuit board, two first lenses and two second lenses mounted above the planar optical waveguide, a base plate electrically connected to the circuit board, and an optical signal emitting member and an optical signal receiving member mounted on the base plate. The planar optical waveguide forms two inclined surfaces. The base plate is positioned above the second lenses. Optical signals are reflected by the inclined surface, and are transmitted to the optical signal receiving member. The optical signal receiving member converts the optical signals to electrical signals to transmit to the circuit board. Electrical signals of the circuit board are converted to optical signals via the optical signal emitting member, and then are transmitted to the planar optical waveguide. The present disclosure further provides an optical transmission connecting assembly using the optical-electrical conversion module.