The enhancement of Ga incorporation into the CIGS thin film by electrodeposition has been realized. One-step electrodeposition Cu(In,Ga)Se2 thin films under different hydrogen peroxide (H2O2) concentrations was investigated. The ratio Ga/(In+Ga) and characteristics of thin films were further modulated by adding H2O2 into electrolyte. The mechanism of the effects of H2O2 on electrodeposition Cu(In,Ga)Se2 thin films was illustrated using a schematic diagram. And this mechanism was proved by cyclic voltammograms, potentiostatic polarization, energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM) and Raman spectra. The films were found to have the same basic chalcopyrite structure of CuInSe2, and have the widen band gap (UV-VIS-NIR spectrophotometer) after adding H2O2 into the electrolyte. The evidence of Ga incorporation increment can be observed from the peak shift of Raman spectra and widen band gap.