In order to explore the reason that polyurea grease is easy to harden at high temperature for a long time,the influence of the structure and composition of organic amines as raw material of the thickener of polyurea grease on the high temperature hardening phenomenon of polyurea grease was analyzed.By means of cone penetration test,thermogravimetric analysis and infrared spectroscopy analysis,the mechanism of high temperature hardening of the prepared biuret,tetraurea and hexaurea grease was investigated.The results show that the thermal stability of polyurea based thickener is obviously higher than that of ordinary biuret grease and the hardening degree of hexaurea grease is the smallest among different urea thickeners at high temperature.Polyaromatic amines can obviously improve the high temperature hardening of polyurea grease.Among the different organic monoamines,the hexaurea greases prepared by mixing alkylamine and aromatic amine have better high temperature resistance and among the different organic diamines,and the grease with diaminodiphenylmethane has the best high temperature resistance.With the increase of working temperature,the N-H and C＝O functional groups of polyurea will be destroyed.The change of urea group structure is the reason for the hardening of polyurea grease at high temperature.