Perfluoropolyether greases are primarily consisted of perfluoropolyether(PFPE)base oils and polytetrafluoroethylene(PTFE)thickeners.The strength of the binding force between PFPE and PTFE molecules is one of the key factors affecting the colloidal stability of perfluoropolyether greases.The special molecular structure of PFPE as well as PTFE determines the weak binding force between molecules,which effects on the colloidal stability of perfluoropolyether greases. In order to improve the colloidal stability of perfluoropolyether greases,hydrophobic fumed silica(S1,S2,S3,S4)with large specific surface area was selected as additives,self-produced,low-viscosity,and branched PFPE was used as base oil,the PTFE powder was used as thickener,and a series of perfluoropolyether greases with different proportions were prepared.The analysis of XRD,SEM and TEM,the test of nitrogen adsorption-desorption isotherm, pore diagram distribution,surface free energy and oil separation from grease were used to investigate the improvement effect of hydrophobic fumed silica on the colloid stability of perfluoropolyether greases.Results show that hydrophobic fumed silica with mesoporous structure has good thickening ability,which improves the colloidal stability of perfluoropolyether grease.Additive S2 with the most specific surface area and pore volume has the most obvious effect on improving the colloidal stability of perfluoropolyether greases.The oil separation of perfluoropolyether grease decreases with the increase of the addition amount of additive S2.Considering the consistency grade requirements of the target grease,the optimal addition amount of additive S2 is 1.5%(mass fraction).