The highest efficiencies for both rigid and flexible Cu2ZnSn(S,Se)(4 )(CZTSSe) solar cells are still far behind the theoretical values. This is mainly due to band tailing in absorber and a large recombination near absorber/Mo interface that block the carrier transportation and lead to Voc and FF degradation, which are mostly noticeable in flexible solar cells. In this paper, CZTSSe thin films were prepared on flexible Mo substrates by green solutionbased method followed by selenization. By optimizing selenization conditions (selenization time and temperature), dense and well crystallized CZTSSe thin films without micro-cracks were obtained at 550 degrees C for 12 min. The best efficiency of 6.78% can be achieved with Voc and FF enhanced to 390.43 mV and 57.71%. The dramatic reductions in ideal factor A, series resistance R-s, the mismatch Delta(Eg-PL) and potential fluctuation gamma indicate that band tailing and recombination are significantly reduced. The performance degradation with bending radius and cycles is studied for the first time among CZTSSe solar cells. Results indicate long-term stability at repeatable release-stretch cycles. The flexible CZTSSe solar cells with high stretch ability shed light on the development of flexible solar cells.