High quality silicon nanowires （SiNWs） were grown directly from n-（111） silicon single crystal substrate by using Au film as a metallic catalyst. The diameter and length of the formed nanowires are 30—60 nm and from several micrometers to sereral tens of micrometers, respectively. The effects of Au film thickness, annealing temperature, growth time and N2 gas flow rate on the formation of the nanowires were experimentally investigated. The results confirmed that the silicon nanowires with controlled diameter, length, shape and orientation can be obtained via reasonably choosing and optimizing various technical conditions. The formation process of the silicon nanowires is analyzed qualitatively based on solid-liquid-solid growth mechanism.