In port crane industry, the surface hardening technique is widely used in order to improve the strength of wheel. From the practical experience, when the high hardness hardened wheel is used, the danger of sudden break of the wheel is increased. How the hardness of the wheel effect the fatigue life of the wheel is not studied theoretically. In this paper, the contact stresses in wheel with different hardness have been analyzed by applying three-dimensional finite element model. Based on this model, the ANSYS10.0 finite element software is used. Three different plastic slopes are used to simulate three different hardness materials. Surface hardened wheel with three different hardness materials, and three different vertical loads are applied. The effect of hardness of a surface hardened wheel is discussed by comparing the contact stresses from the numerical results. The reason of the sudden failure of the high hardness hardened wheel is discussed, and some suggestions are given in choosing hardness of the hardened wheel.