Strong anisotropy of physical and mechanical properties of Potassium Dihydrogen Phosphate (KDP) crystals significantly affects surface quality during processing the samples. Different processing direction, along , , and  crystallographic orientations, are chosen on (001) crystal plane in order to evaluate the anisotropic characterizations on the processed surface. Scanning electronic microscopy (SEM) is employed to observe the machined surface damage, defects and profiles. At the same time, surface quality is measured by Zygo surface profiler to estimate the processed surface quality. The results show that the machined surfaces along three different orientations under the same processing conditions behave quite differently from each other. Strong anisotropy and complex slip system of KDP crystals lead to several different asymmetric damages on the machined surface. Surface roughness (Ra) values along  are the smallest, that along  are in average, and that along  are largest. Moreover, many illustrations are given to understand the anisotropic nature during processing, including slip system, mechanical properties during processing, and technical parameters, etc.