As a typical single crystal material, the ground surface characteristics of sapphire are influenced by the relationship between machining direction and crystalline orientation. In this paper, the effects of grinding direction on the surface characteristics of the prism-plane sapphire were investigated by a series of sapphire grinding experiments under the orthogonal machining directions. The ground surface topography, surface layer lattice residual stress and degree of lattice distortion were measured. The results show that the grinding force with the grinding direction along the c-axis is greater than the grinding force along the m-axis or the a-axis, and serious damage was generated to the ground surface with grinding direction along the c-axis. The full width at half maximum intensity value of the X-ray rocking curve indicates that the residual stress of the ground surface with machining direction along the c-axis is greater than that along the m-axis or the a-axis, and the molten KOH etching analysis results manifest that the degree of lattice distortion of the ground surface with machining direction along the c-axis is higher than that along the m-axis or the a-axis. Therefore, the grinding direction along the m-axis or the a-axis is better suited to process prism sapphire.