In this paper,we investigate ZnO thin films on PEN DC magnetron sputtering at room tempurature.At different sputtering power values and pressures,the ZnO thin films exhibit different optical and electrical properties.Optimizing sputtering power and pressure,we find the optimal ZnO film on PEN substrate,whose thickness is 900 nm,resistivity is 7.72×10-4 Ω·cm,and average transmittance in the range 400-800 nm is over 75%.We use it as the surface electrode of amorphous silicon thin film solar cells and finally get flexible cells with conversion efficiency of 6.4%.