The invention relates to a method for protecting a water solution growth crystal surface step. The property that KDP (Potassium Dihydrogen Phosphate) is not dissolved into n-hexane and chloroform and physical properties that the density of the n-hexane is less than that of water and the density of the water is less than that of the chloroform are utilized, and the water solution left on the surface of a crystal is removed, so that the integrity and accuracy of the shape of the growth step are guaranteed, and the crystal is safely and effectively preserved. Before an organic solvent is used, the water solution is heated to a temperature similar with the temperature of a growth solution as much as possible, and thus cracking of the crystal, caused by too great temperature difference, is avoided. The method provided by the invention can be used for completely avoiding damages caused by a process of removing the water solution attached on the surface of the crystal, and re-crystallization of residual solutes on the surface of the crystal and damages to a surface structure are not caused. The working difficulty can be reduced when a complete and clean surface is found in an experimental test, and the integrity and accuracy of the shape of the growth step are guaranteed.