Four kinds of amines co-initiator with different structure were synthesized in Michael-Addition reaction with aliphatic amine and trimethylolprpane triacrylate (TMPTA). The photo-polymerization of tripropylene glycol diacrylate (TPGDA) / benzophenone (BP) / amine co-initiator was investigated by real-time infrared spectroscopy (RTIR). The yellowing of BP/amine co-initiator during UV curing was characterized by ultraviolet spectrophotometer. The results show that the increment of the content of hydroxyl group leads to the decrement of the photopolymerization rate. And the photo-polymerization rate decreases with the increment of molecular weight for the equal hydroxyl content. But there is no change with the double bond conversion. It has been demonstrated that the amines co-initiator with tertiary amine structure can cause higher yellowness index (YI) and faster yellowness index growth during UV irradiation than that with secondary amine structure. And the YI also increases with the increment of the content of hydroxyl group in the amines co-initiator. Lower yellowness index amines co-initiator could be synthesized based on the results obtained in this paper.