We developed a way primarily based on the mechanically controllable break junction approach to analyze the electron transport properties of single molecular junctions upon fiber waveguided mild. In our technique, a metal-coated tapered optical fiber is fastened on a versatile substrate, and this tapered fiber serves as each the optical waveguide and metallic electrodes after it breaks. For an imidazole bridged single-molecule junction, two possible conductance values under 1Gzero are noticed. The upper worth exhibits an roughly 40% enhancement beneath illumination, whereas the decrease one doesn’t present distinguishable distinction beneath illumination. Theoretical calculations reveal these two conductance values ensuing from the imidazole monomer junction and the imidazole dimer junction linked through a hydrogen bond, respectively. In imidazole monomer junctions, the absorption of a single photon strongly shifts the transmission operate leading to optical-induced conductance enhancement. In distinction, the transmission operate of imidazole dimer junctions stays on the identical degree within the bias window regardless of the sunshine illumination. This work offers a strong experimental framework for finding out the underlying mechanisms of photoconductivity in single-molecule junctions and gives instruments for tuning the optoelectronic efficiency of single-molecule units in situ.