The lithium niobite (LNO) single crystal thin film prepared by high-energy ion implantation and stripping has excellent electro-optical, acousto-optic properties, and is in urgent need in the fields of radio frequency devices and optical waveguides. However, the high-energy ion implantation leads to the existence of a damage layer on the surface of the LNO single crystal film, which results in the degradation of film quality and device performance. A method for removing damaged layer of LNO single crystal thin film by Ar+ etching is proposed in this paper. Based on the simulation of high-energy ion implantation, the influence of etching parameters on the etching rate and surface morphology are analyzed by scanning electron microscope and atomic force microscope, and the etching parameters of the damaged layer of LNO film are determined. The X-ray diffraction analysis shows that the full-width at half maximum height of the rocking curve of the LNO film with Ar+ etching is reduced to near that of the LNO single crystal material before implantation. The results of the piezoelectric force microscopy tests show that the LNO single crystal film after removing the damage layer has a more consistent piezoelectric response.