The purpose of this paper is to obtain an insight into the effects of shear keys with different slopes on the nonlinear seismic responses of an arch dam. The nonlinear exponential dynamic contact constitutive model is proposed for simulating the normal interactions of the two surfaces separated by contraction joints, along with the standard Coulomb friction model to simulate the tangential interactions. After the shear key’s real configuration is established, the seismic responses of the arch dam are discussed in detail to understand the effects of shear keys on the behavior of the contraction joints and the stress and deformation of the dam. The results indicate that the dam without the shear keys shows comparatively narrow joint opening, and that the maximum joint opening decreases when the slope of shear keys increases. In addition, the slope of shear keys exerts an obvious effect on the sliding displacement along the radial direction and the stress of the dam.