Cu2ZnSn(S,Se)(4) (CZTSSe) chalcogenide with natural-abundance, environment-friendly and impressive photovoltaic performance is promising material for kesterite thin film solar cell. In this paper, the effects of evaporated Sb layer on performance of flexible CZTSSe thin film solar cell are investigated. Systematic studies show that the quasi-liquid Sb2Se3 plays productive roles in promoting grain growth, subsequently volatilizes in the elevated selenization temperature without entering into the CZTSSe lattice. Obvious improvements in crystallinity, grain size, surface roughness, hole concentration and device performance are obtained after optimizing the thickness of Sb layer. The electrostatic potential fluctuation extracted from the PL results is found to decrease from 115.9 meV to 60.7 meV after introducing 20 rim evaporated Sb layer. Finally, 20 nm evaporated Sb layer takes effect to the fullest extent which shows a 69% increase in photoelectric conversion efficiency (PCE). The incorporation of Sb opens up access to opportunity in roll-to-roll process for thin film solar cells.