We fabricated the Cu2ZnSn(S,Se)4 (CZTSSe) absorber with S-modified surface. The effects of surface sulfurization on CZTSSe were thoroughly investigated. Enlarged surface bandgap and reduced interface recombination enhance the Voc. Surface localized electric properties are improved due to surface passivation. The efficiency of CZTSSe device increases from 5.01% (without) to 7.38% (with H2S).