The lead halide perovskite nanocrystals (NCs) have become more ideal luminescent materials due to the excellent properties such as narrow emission linewidth, photoluminescence quantum yield (PLQY), adjustable spectrum and facile preparation in comparison with traditional II-VI or III-V group semiconductor NCs. Until now, the external quantum efficiency (EQE) of light-emitting diode (LED) devices using perovskite NCs as emitting layers, has reached > 20%. This optical performance is close to that of the commercially available organic LED, which shows their great potential applications in solid state lighting and panel displaying. However, when perovskite NCs suffer light, heat and polar solvent, they exhibit the poor stability owing to the intrinsic ion properties of perovskite, and highly dynamic interface between NCs and ligands as well as the abundant defects on the surface of NCs. Therefore, how to elevate their stability is a key and urgent problem. In this review, three methods to improve the stability of NCs are summarized: 1) In situ surface passivation with tight-binding or protonation-free sole ligands such as oleic acid (OA), oleamine (OAM), dodecyl benzene sulfonic acid, octylphosphonic acid, sulfobetaines, lecithin and two ligands such as 2-hexyldecanoic acid/OAM, bis-(2,2,4-trimethylpentyl)phosphinic acid/OAM as well as three ligands such as OA/OAM/Al(NO₃)₃·9H₂O, OA/OAM/tris(diethylamino)phosphine); the postsynthetic ligand exchange or passivation with 1-tetradecyl-3-methylimidazolium bromide, 2-aminoethanethiol, silver-trioctylphosphine complex and n-dodecylammonium thiocyanate; 2) the doping of Cs⁺ by FA⁺, Na⁺ and the doping of Pb²⁺ by Zn²⁺, Mn²⁺, Cd²⁺, Sr²⁺, Sb³⁺ in perovskite NCs; 3) the surface coating with inorganic oxides (SiO₂, ZrO₂, Al₂O₃, NiO_x), inorganic salts (NaNO₃, NH₄Br, PbSO₄, NaBr, RbBr, PbBr(OH)), porous materials (mesoporous silica, zeolite-Y, lead-based metal-organic frameworks), polymer materials (polystyrene, poly(styrene-ethylene-butylene-styrene, poly(laurylmethacrylate), poly(maleic anhydride-alt-1-octadecene), polyimide, poly(n-butyl methacrylate-co-2-(methacryloyloxy)ethyl-sulfobetaine)). Besides, we make some suggestions to further improve the stability of NCs as follows: 1) Developing the surface ligands with good dispersity and multi-coordination groups; 2) theoretically studying the influence of ion doping on the structure and stability; 3) realizing the stable and conductive metal oxides shell for uniform and compact encapsulation of NCs core. In a word, these conventional methods can enhance the stability of NCs to a certain extent, which fail to meet the requirements for practical application, so more efforts will be needed in the future.