Display omitted •Synergistic suppressing mechanism was illustrated to explain the strong suppressing ability of Brilliant Green on copper electrodeposition.•The strong suppressing effect of Brilliant Green was confirmed by electrochemical tests.•Copper superconformal electrodeposition was achieved and high FP values (80.52 % to 84.38 %) with low SDT (about 28 μm) was obtained in the optimized condition. Finding proper additive to achieve copper superconformal electrodeposition is significantly important. Brilliant Green exhibits excellent suppressing ability to the copper electrodeposition according to electrochemical analysis. Meanwhile, 100 mg/L was selected as the optimum value based on the convection-dependent adsorption behavior analysis of Brilliant Green. The interaction among three different additives was also investigated by applying chronopotentiometry as well as Brilliant Green compete to absorb on the cathode surface with SPS. Besides, the introduction of Brilliant Green can improve the transport of cupric ions (Cu2+). The nucleation and growth of copper deposition is 3D diffusion-controlled instantaneous growth process at high overpotential but 3D diffusion-controlled mixing growth process at low overpotential. The synergistic suppressing mechanism was proposed to explain strong suppressing effect of BG on reduction of Cu2+ and the reaction pathways was studied theoretically. Copper interconnect layer with high FP values (80.52 % to 84.38 %) was obtained with low SDT (about 28 μm) after electroplating process was optimized. The surface morphology under the influence of Brilliant Green is compact and uniform and the grain size is reduced by Brilliant Green.