The existing defects on the surface of CsPbX3 nanocrystals (NCs) resulted in the decrease of the photoluminescence quantum yields (PLQYs) of NCs. In this study, we developed a simple strategy, which can make the treated CsPbX3 NCs exhibit high PLQYs and better stability by CdX2 post-treatment at room temperature. The treated CsPbX3 NCs were characterized by X-ray diffraction (XRD) patterns and PL spectra. The shape, size, and crystal structure of the NCs remained unchanged after Cd ion treatment. The PLQYs of CsPbCl3 increased from 24 to 73% and the PLQYs of CsPbBr3 NCs increased from 85 to 92% after treatment. The significant enhancement of PLQYs is ascribed to the effective passivation of surface defects, in which Cd2+ and X- ions occupied the Pb-X vacancies existing on the surface of the NCs. In addition, this strategy was also applied to a mixed halide perovskite. The practical application of CsPbX3 NCs will be extended by this method.