Cement-based materials typically have a relatively high compressive strength and a relatively low tensile strength. In this paper, multiscale silicon carbide whiskers (SW) were used to improve mechanical properties of oil-well cement stone. The structure and properties of whisker cement stone were analyzed via mechanical testing and cement sheath integrity. The results demonstrated that multiscale SW mixing showed a positive hybrid effect and could effectively improve the compressive strength, the flexural strength, and the splitting tensile strength of oil-well cement stone by 8.96%, 137.44% and 27.96%. The modulus and porosity of the whisker cement stone significantly reduced. The filling effect, whisker pinning, the pullout, and the whisker bridging were regarded as effective mechanisms for the addition of SW when improving the mechanical properties and microstructures of oil-well cement stone.