The study used a fatigue test model to investigate the surface fatigue strength of a specific carburized gear material, i.e. AISI 4118. A set of test specimens is designated to simulate the mechanics of gear tooth meshing. A friction, wear, and tribological tester is used to conduct the surface contact stress generated between the test specimens. The surface fatigue lives of the test specimens under different levels of contact stresses have been detected. Based on the maximum likelihood method proposed by Ling and Pan, the R-S-N curves of the surface durability of the specific material have been established using the experimental data of the fatigue test. Especially the fatigue strength for long fatigue lives at required reliability can be estimated.