The invention belongs to the technical field of preparation of hindered amine light stabilizer midbody and pharmaceutical midbody triacetonamine, and particularly relates to a method and a special device for heterogeneous catalyzed synthesis of triacetonamine. The technical scheme is that a cone base reaction kettle consisting of a straight cylinder section and a cone cylinder section is applied, and a water knockout drum formed by a tubular type membrane tube is arranged in the cone base reaction kettle; heterogeneous catalyst and acetone are added in the reaction kettle; after stirring and heating, ammonia gas is filled for reaction; the procedures of separating water by the water knockout drum, cooling, stopping mixing, separating water and standing are carried out, and reaction fluid is discharged and filtered to obtain a crude product of triacetonamine; finally, the crude product is rectified to obtain the high-purity triacetonamine product. In the invention, the heterogeneous catalyst is applied to replace the homogeneous catalyst, thus the separating difficulty of the catalyst is reduced, the high saline-alkali waste water generated from separation process of homogeneous catalyst is avoided; the reaction water is separated from the reaction process, the yield of triacetonamine is improved, and the water separating cost of the rectifying technique is reduced. The content of organic matters in separated water of the water knockout drum is low, and water disposal cost is reduced.