NOVELTY - A copper-zinc-tin-sulfide based nanocrystalline thin film preparing method involves dissolving tin salt and complexing agent in the first solvent to obtain solution A, dissolving sulfur and/or selenium source in the first solvent to obtain solution B, stirring solution A and B, centrifuging and drying to obtain tin based nano-crystal particle, preparing zinc and copper based nano-crystal particle. The tin-zinc-copper based nano-crystal particle is dissolved in second solvent to obtain precursor. The precursor is coated on a substrate, followed by heating to obtain finished product.    USE - Method for preparing copper-zinc-tin-sulfide based nanocrystalline thin film that is utilized for absorption layer of solar energy battery.    ADVANTAGE - The method enables preparing copper-zinc-tin-sulfide based nanocrystalline thin film with increased conversion efficiency in an eco-friendly manner.    DETAILED DESCRIPTION - A copper-zinc-tin-sulfide based nanocrystalline thin film preparing method involves dissolving tin salt and complexing agent in the first solvent to obtain solution A, dissolving sulfur source and/or selenium source in the first solvent to obtain solution B, stirring solution A and solution B, and centrifuging to separate solid material, washing the solid material and drying to obtain tin based nano-crystal particle, dissolving zinc salt and complexing agent in the first solvent to obtain solution C, dissolving sulfur source and/or selenium source in the first solvent to obtain solution D, stirring solution C and solution D at 100-200 degrees C for 1-20 hours, and centrifuging to separate solid material, washing the solid material and drying to obtain zinc based nano-crystal particle, dissolving copper salt and complexing agent in the first solvent to obtain solution E, dissolving sulfur source and/or selenium source in the first solvent to obtain solution F, stirring solution E and solution F, and centrifuging to separate solid material, washing the solid material and drying to obtain copper based nano-crystal particle. The tin-zinc-copper based nano-crystal particle is dissolved in second solvent to obtain precursor. The precursor is coated on a substrate surface, followed by heating the surface under nitrogen or argon air atmosphere to obtain finished product, where the first solvent is deionized water, ethanediol, triethanolamine or methyl alcohol, the second solvent is methyl alcohol, ethyl alcohol, ethanediol, ethylene diamine or dimethyl sulfoxide.