Thin DLC film is in need for higher magnetic storage density. Surface modification and materials removal of DLC films were carried out in order to estimate the reliability of the ultra thin DLC films. Atomic force microscope (AFM) was used to investigate the wear resistance, surface modification and mechanical reliability of the films. Wear test by contact AFM indicated that wear depth under the same load was varied at different thick films. The local modification is studied using conductive atomic force microscope (C-AFM). Especially, topography change is observed when DC bias voltage applied. Experimental results show that the DLC surface is not modified after direct current applied on the tip. While positive voltage is applied on the DLC film surface, the nanoscale pit on the surface is formed clearly. According to the interaction force between CoCr coating MESP tip and the DLC film surface, as well as the Sondheimer oscillation theory, the “scale wing effect” of the pit is explained. Electromechanical coupling on the DLC film indicates that the depth of pit increases with the augment of force applied on surface when normal force is less than a certain threshold pressure.