In this paper, ultrafine CL-20 was prepared by wet grinding procedure. The morphology, particle size, sample composition, and crystal structure of CL-20 before and after grinding were detected by scanning electron microscope, laser granulometer, infrared Raman Spectroscopy, and X-ray diffraction instrument. The thermal decomposition, mechanical sensitivity, shock wave sensitivity, flame sensitivity, bulk density, and rheological property of CL-20 based explosives were tested. The results indicated that the crystal form of CL-20 was retained as epsilon-form after wet grinding. The ground CL-20 was superior in physical properties to the raw CL-20, such as smaller particle size, smooth surface, less mechanical sensitiveness, and lower flame sensitivity. However, the thermal stability was slightly decreased. Moreover, the bulk density of ground CL-20 was higher, which leading to an increase in density of shaped charge column. The viscosity of the CL-20 based cast explosive formulation was effectively reduced, that can improve the process of explosive formulation and the process adaptability. In addition, under high strain rate loading, the impact safety of the explosive prepared with ground CL-20 is improved.