Abstract: The wear mechanism of GM-3 friction liner was studied using a high-strength transparent toughened glass as the counterpart. The reciprocating friction experiments were conducted on a Rtec friction machine. With the adoption of in-situ observation method(using VW9000 high-speed microscope camera) and the gray-scale method, the real contacting area was calculated. The results of the experiments show that the friction coefficient was proportional to the real conducting area. The wear mechanism in the initial period was abrasive wear and adhesive wear while it was fatigue wear after the initial stage. The initial abrasion wear led to the increase of friction coefficient with the formation of scroll-shaped debris. In the later stage, friction coefficient tended to be stable accompanied by increased size and decreased amount of debris as a result of the aggregation of the small one.