The hindered amine light stabilizer 625 was synthesized by methylation reaction from hindered amine light stabilizer 360 and paraformaldehyde in toluene, and the structure was elucidated by 1HNMR. Via the single factor experiments and the orthogonal experiments,the suitable methylation conditions were obtained as follows, n(360):n(formaldehyde)=1:4.6, the reaction temperature was 85℃, and the reaction time was 6h. Under these conditions, the methylation rate was 97.4%. Compared with the formalde-hyde/formic acid method, formic acid wasn’t required inthe reaction. The method avoided the problem of salt-forming agglomeration of the light stabilizer 360 with formic acid and of the cumbersome workup, simplified the operation, reduced the cost. It has the advantages of higher methylation rate and lighter product color.