This study is focused on the technique for fabrication of high aspect ratio nanostructures by combining both the advantages of maskless patterning of focused ion beam (FIB) and anisotropic etching of inductively coupled plasma etcher (ICP) in CF4 atmosphere. The materials contain p-type (100) single crystal silicon and thermal silicon dioxide. The study details include¡G (1) The reliability of AFM when scanning isotropic and anisotropic nanostructures with high aspect ratio tip in tapping mode. (2) FIB direct writing test. (3) The influences of ICP parameters including ICP power, bias power, content of oxygen, and process pressure. After completion of above-mentioned items, an optimized condition is used to get the anisotropic Si-based high aspect ratio nanostructures of holes array, gratings and cylinder under 100nm. The smallest line width of single crystal silicon gratings is 48nm, and aspect ratio up to 2.36. The smallest line width of silicon dioxide gratings is about 100nm, height is 410nm and aspect ratio up to 2.36 measured by SEM. By combining both advantages of different systems, we can provide another simple and rapid method for nanofabrication.