Abstract: KDP is a type of excellent nonlinear single crystal electro-optical material, which is used in high-energy laser systems. However, KDP is extremely difficult to be finished for its particular physical and chemical properties. Magnetorheological finishing (MRF) is considered to be an effective processing method for finishing KDP to high precision at present. But the performance of KDP would decrease obviously if the residual contamination remained after finishing. An active cleaning agent with high-frequency ultrasound technology was put forward to solve the problem. Microscope and white-light-interferometer were employed to assess the effects of cleaning process on KDP surface. The results show that the residual contamination is removed availably, and the surface roughness is improved as well. Additionally, the Raman spectral and laser interferometer analysis indicates that crystal structure and surface accuracy of KDP remain unchanged after cleaning. These conclusions prove that the cleaning method achieves desired result and exhibits a promising prospect of KDP cleaning.