The formation of polyisocyanurate-oxazolidone(PISOX) has been systematically studied The influences of the reaction temperature and the ratio of isocynate and epoxy to the gene ration of oxazolidone(OX) and isocyanurate(IS) rings in the formation of PISOX were quanti fatively investigated by means of in-situ infrared spectroscopy. It is found that low tempera ture is suitable to the generation of IS ring and high temperature is favorable to the generatioi of OX ring. At higher temperature IS ring may open and transform into OX ring with epoxy group. The structure of PISOX is mainly deterrined by the ratio of isocynate and epoxy and also the curing technology.