Abstract: Wear of the casing as occurring during deep well and ultra-deep well drilling operation produces a direct negative influence on integrity of the well hole.The full-scale casing wear tester is used to simulate the mechanical conditions of the actual drilling operation.Performed are the friction/wear tests to the drill pipe joint with the Arnco 100XT hard facing and the inner surface of the 140 casing in three different types of high-density oil-base mud,and the friction surface of the casing is analyzed by the SEM,and thus key friction and wear parameters such as wear volume,friction coefficient and wear factor are obtained.The test results show that when the density of oil-basemud is increased to 1.78 g/cm³ by barite merely,the wear mechanism is abrasive wear,and the wear level is slight;and when the mud is further increased to 2.20 g/cm³ and 2.41 g/cm³ by 1:1 proportioned-barite and iron ore powder mixture,the wear mechanism changes to abrasive wear and adhesive wear as co-exist,and the wear level is rather serious.Compared with operation in the low density oil-base mud,the casing wear as caused with operation in the high density oil-base mud is deemed as slight.