The structure, optical and electrical properties of the CdTe polycrystalline thin film prepared by close-space sublimation and doped with rare earth element erbium using ion implantation had been investigated by means of X-ray diffraction, scanning electron microscopy, ultraviolet visible spectroscopy, Hall effect and impedance measurement. The results indicate that the crystallinity of the samples can be improved with suitable doping concentration. It is believed that the grain-boundary barrier of the thin film CdTe:Er can be decreased due to the appearance of electron traps at grain boundaries. It is found that the implantation of Er3+ in CdTe thin film causes a great change in conductivity but only a little influence on optical energy band gap of the samples.