Thermal spraying of WC-Co cermet was applied on annealed or quench-tempered tool steel substrates by a high-pressure high-velocity oxygen fuel method. Rolling contact fatigue tests were carried out under the loads of 2000, 3500 and 5000N, and delamination energy was obtained by an edge-indent test. After certain numbers of rolling contact cycles, pitting cracks appeared on the surface and preexisted cracks in the coating propagated in a direction parallel to the interface. For the annealed substrate, many cracks were formed in the coating vertical to the interface under the rolling load of 5000N. The delamination energy was larger for the annealed substrate than the quench-tempered substrate before tests, but it decreased with increasing number of rolling contact cycles for the annealed substrate than the quench-tempered substrate. The results of a finite element method reveal that large shear stress and tensile plastic strain exist near the interface, which means that the fatigue damage due to the repeating stress and strain have caused the decrease in delamination energy.