Pure titanium substrate specimen was sputter-coated with SiC or CoCrNi-oxide thin film and the wear test was carried out by using a “ball-on-disk” type testing machine. The semi-circular parallel cracks appeared on the film surface with angles of 45 degree to the sliding direction of the SiC ball and the delamination of film quickly occurred after the cracking. With the aid of finite element methods, stress distribution before and after cracking in the film was obtained. The maximum tensile stress existing in the film at the back-contact edge of ball is the reason for the initiation of semi-circular parallel cracks. After the film is cracked, the tensile stress normal to interface as well as the shear stress along interface appear at crack tip. The combination of these two stresses is the main reason for the delamination after the film is cracked.