Abstract: The hardness of the residual decarburized layer is lower than that of the tempered martensitic matrix. Due to the small amount of the residual decarburized layer, its influence on the overall mechanical properties of the sample is not significant. In addition, its metallographic structure is similar to that of the surface white layer by machining, and thus it is difficult to identify. As a result, researchers tend to neglect the effect of a small amount of residual surface decarburized layer. In the present work, the effect of residual surface decarburized layer on rolling contact fatigue (RCF) failure mechanism of bearing steel was studied by simulating the service environment of thrust bearing with a ball- and disc-type RCF tester. The results show that a small amount of residual surface decarburized layer not only reduces the RCF life of bearing steel, but also significantly increases the dispersity of fatigue life. The main failure mechanism of bearing steel is as follows: In service, near-surface cracks initiating in the decarburized layer and surface cracks induced by surface abrasion accelerate the RCF failure process, resulting in the decrease of RCF life and the dramatic increase of fatigue life dispersity.