Cationic doping is considered to be an effective way to improve the efficiency of Cu2ZnSn(S,Se)4 (CZTSSe) photovoltaic materials. To improve the quality of the absorption layer of the crystal film, CZTSSe film was doped with some Cd2+ ions to change the ratio of Cd and Zn in the precursor solution. X-ray diffraction (XRD), Raman, scanning electron microscope (SEM), ultraviolet-visible (UV-Vis) spectroscopy and other results showed that Cd successfully replaced Zn in the crystal lattice during post-selenization. The formation of harmful Zn-related defects was reduced, the grain size and crystallinity of the films were significantly increased, and the photoelectric properties of the films such as crystal quality and structural morphology were improved. As the Cd/(Cd+Zn) ratio increased from 0 to 0.35, the band gap of CZCTSSe decreased to 1.02 eV. When Cd/(Cd+Zn)=0.25, the crystallinity and grain size reached the best value, and the film surface was smooth and dense, which inhibited the formation of the second phase on the surface of CZCTSSe. The theoretical basis and experimental results showed that proper Cd doping can promote the growth of grain, so that compact CZCTSSe films with larger grain sizes and fewer holes could be prepared.