The cutting-off ability of diamond abrasive wire is experimentally studied. The wire has one layer of diamond abrasives around the core steel, so the cutting-off ability of the wire is continuously decreased due to falling off and wear of abrasive grains, and no recovering of the initial cutting-off ability is reached. It may be generally said that simple cutting-off ability of the wire is low compared with that of cutting wheel. But the wire can even cut off ceramics well while most abrasive grains keep sharp edges. And it is experimentally confirmed that ; machining without coolant shows much lower cutting ability than that with coolant ; ratio of tangential force to normal force is decided by material of workpiece and wear of abrasive wire, while it is slightly depended on wire running speed ; wire tension and normal force. The ratio evidently affected with material ductility, for example 0.5 for alumina-ceramic, 0.54-0.55 for glass, 0.68-0.74 for brass and 0.8-0.87 for aluminum without apparent wire wear. The machining characteristics of diamond abrasive wire are simply represented by the ratios of cutting-off area to unit grinding forces and unit wire running length.