The utility model discloses a system for preparing a micro nano structure silicon, which is characterized in that a reflector, a continuous adjustable attenuation sheet, a light shutter, a lens and a three dimensional adjusting bench are fixed an optical platform; a stainless steel long chamber vacuum chamber is installed on the three dimensional adjusting bench, and the front end of the stainless steel long chamber vacuum chamber is provided with a window sheet, and the internal back surface is pasted with silicon chips, and the external part is connected to a vacuum chamber gas filled pipe; the pipeline is arranged two micro-adjustable valves, and the light shutter is connected to a pulse counter through a lead. Incident laser power is adjusted by the continuous adjustable attenuation sheet, and the etching pulse quantity is accurately controlled by using a pulse counter in cooperation, and gas pressure in the vacuum chamber is adjusted by using the micro-adjustable valve, finally micro nano structure silicon materials of various appearances are formed. The utility model has the advantages of simple production technology and convenient operation, and the silicon material of micro nano structure has an absorption spectrum with a span exceeding 2500nm, and the reflectivity is lower than 10%.