The invention belongs to the technical field of macromolecular material performance additives, and particularly relates to a light stabilizer and a preparation method thereof. The preparation method comprises the steps: using morpholine, N-butyl-2,2,6,6-tetramethyl-4-piperidinamine, 2,4,6-trichloro-1,3,5-triazine(cyanuric chloride), N,N'-bis(3-aminopropyl)ethanediamine and an alkali as raw materials, selecting xylene, methylbenzene or chloroform as a solvent for reaction, and synthesizing a novel light stabilizer through controlling the reaction temperature, adjusting the suitable feed ratio and pressurizing to promote the reaction. The light stabilizer has the advantages of pesticide resistance, low alkalinity and small environmental pollution, has good intermiscibility with most industrial solvents, and has excellent macromolecule intermiscibility. The light stabilizer can be added into plastics, rubber or coatings to relieve the aging and decomposing and extend the service life. In the processing and using, peculiar smell cannot be generated, and the original color of the materials cannot be affected. The light stabilizer has the advantages of high temperature resistance, difficulty in volatilization, excellent stability and low cost.