Abstract: Casing wear was investigated on the DCWT-1000 casing wear tester, the influence of impact -slide of deep and ultra-deep well on the wear behavior of casing was studied. Microstructure and surface topography of the wear surface of casing under different loads were investigated by means of 3 D surface topography measurement apparatus, microscope, and SEM. 3D topography of wear surface of casing was rebuilt and the main topography parameters were calculated, and the wear mechanism of casing was discussed. It is found that the load intimately correlated with wear property and surface topography parameters of wear surface of casing. 3 D topographies of wear surface of casing were different under different loads, there was better correlation between the main topography parameters and the load, and it is proved that the 3 D topography analysis can more truly reflect the casing wear. The abrasive wear mainly occured under small load, and sometimes the adhesive wear appeared too, peeling due to adhesive wear and fatigue wear was seen obviously, and the fatigue crack appearred development and join, the casing wear mechanism changed to surface fatigue and adhesive wear, the casing wear becomes more serious.