The invention discloses a preparation method of an L-histidine glyoxal bis-Schiff base nickel complex. According to the invention, L-histidine glyoxal bis-Schiff base can be prepared by using L-histidine and glyoxal as raw materials and methanol as a solvent without adding a catalyst, then, L-histidine glyoxal bis-Schiff base iss used as a ligand, and is reacted with nickel chloride in an aqueousmethanol solution to prepare the L-histidine glyoxal bis-Schiff base nickel complex. The method of the invention has the advantages of no need to add the catalyst, simple process, good repeatability and high yield, and is applied to photocatalytic degradation of a methylene blue solution with good effect.