As an emerging semiconductor, environmentally friendly thermoelectric material, Cu2Se has drawn great attention due to its outstanding thermoelectric performance. In this work, Cu2Se-based thin films were deposited on a flexible polyimide substrate by magnetron sputtering technique via in-situ growth method. The effect of growth temperature and Cu composition was investigated. The results indicate that the thin films grown at 200 °C have high electrical conductivity due to their high carrier mobility. Further adjusting of Cu composition can achieve highly (0l0)-preferred orientation Cu2Se-based thin films with optimized carrier concentration, resulting in an increase in Seebeck coefficient and further leading to the enhancement of power factor.