A sequential surface adsorption method for improving the photostability of perovskite nanocrystals (NCs) at room temperature was proposed. Firstly, S2- was decorated on the surface of CsPbBr3 NCs by adding didodecyl dimethylammonium sulfide (S2--DDA+), and then In3+ ions, which diffused from the salt powder of In(Ac)3, were slowly adsorbed by the pre-loaded S2-. Through this process, the photoluminescence quantum yield of the CsPbBr3 NCs increases from 57% to 80%, and their photostability, thermal stability, and colloidal stability were all drastically improved. The resultant CsPbBr3·S-In NCs remained stable for 188 h under strong LED light illumination (450 nm and 175 mW cm-2), while pristine CsPbBr3 NCs totally quenched in 2 h, which shows the great potential of CsPbBr3·S-In NCs in lighting and display applications. We also demonstrated that this method could be extended to many other metal salts to form stable perovskite·S-X (X = Ni, Mn and Zn) nanocrystals.