Abstract: A cermet additive in lubricating oil with main composition was Al_4 Si_4O_(10)(OH)_8,as added into all the twelve practical Cr-plated cylinder liners of the locomotive DF7D0062.After a long time(260 000 km) running,the anti-wear and self-repairing effects of the additive were studied by comparing the inner diameter variation of different parts of the cylinder liners before and after the test.The cermet additive exhibited obvious anti-wear and self-repairing function,and it well covered the micro-cracks on the surface,obviously reduced the roughness,and greatly improved the lubricating property.A 250~450 nm repaired layer with a carbon-rich layer and a transition layer was unevenly distributed on the frictional surface.The carbon-rich layer was supposed as in DLC structure.The additive played a key role in the running process by the complex catalytic action instead of being part of the repaired layer.