Abstract:High temperature or impact load can cause the leakage of drilling fluid into the composite lithiumbased grease,thus affecting the lubrication and friction and wear properties of rock bit journal bearings.The rheological test of the composite lithiumbased grease mixed with different mass fraction of drilling fluid was carried out by using MCR102 Rotary Rheometer,and the unit tribology test for journal bearing under the simulated operating condition of rock bits was carried out to analyze the effects of drilling fluid contaminated lubricating grease on the tribological properties of rock bit journal bearings.The results show that the contamination of drilling fluid will reduce the viscosity of grease and change the rheological properties of grease.In general,the contamination of drilling fluid increases the friction coefficient of journal bearing unit and the fluctuation range of friction coefficient,and increases the wear of the bearing.And at high rotational speed,the lower content of drilling fluid in grease will result in the maximum friction and wear of journal bearing unit.Abrasive wear and furrow effect caused by ultrafine calcium carbonate and barite particles in drilling fluid may lead to rapid failure of journal bearings.