7-hydroxy-4-methylcoumarin was synthesized by resorcinol and ethyl acetoacetate under the catalysis of concentrated sulfuric acid. Then 4-nitro-phthalimide as raw materials was first in the open-loop catalytic ammonia and then by the dehydration with phosphorus oxychloride to get 4-nitro-phthalonitrile. The two obtained compounds by nucleophilic substitution reaction were reacted to form 7-(3,4-dicyanophenoxy)-4-methylcoumarin. By investigating the feed ratio, the amount of acid binding agent, the reaction temperature and reaction time, we confirmed the optimal reaction conditions which were 7-hydroxy-4-methylcoumarin,4-nitro-phthalonitrile and anhydrous potassium carbonate whose molar ratio were 1.4:1.0:1.5 , the temperature 30 ℃, reaction time 14 h and the yield 63.7%. And the structures of compounds synthesized have been confirmed by IR, 1H-NMR and high performance liquid chromatography(purity 99.30 %).By enlarging the experimental conditions, we get the yield about 83.1% which is higher than the reported yield 68%.