The conical array on the surface of ultra-light-trapping black silicon, which is divided into five layers, is designed using the equivalent medium theory. It′s considered that the refractive index of silicon varying with the wavelength. The elements which affect the reflectivity are analyzed systematically using the rigorous coupled-wave theory, such as incident angle, the height of the conical array and the duty factor. According to the simulation, the reflectivity is always less than 5% when the incident wavelength is from 300 to 1200 nm and the incident angle is from 0° to 60° with the conical array′s period of 135 nm and its height of 480 nm.