Electroless metal deposition is a simple, low-cost and effective method for fabricating silicon nanowire arrays and has been used widely in micro electromechanical industry. In this paper, large-area silicon nanowire arrays are prepared successfully with mixed AgNO3 and HF solution by this method at normal temperature and pressure. It has been proved the best equality of silicon nanowires can be obtained at the concentration ratio of 0.02 mol/l: 5mol/l for AgNO3 and HF and 1h reaction time. The influence of nano metal particles on the growth, the wire diameter, the distribution and the array of silicon nanowires are analyzed. Experimental results show the distribution and wire diameter of silicon nanowires can be controlled effectively by nano metal particles deposited on silicon wafers. The length of silicon nanowires increases with the reaction time and the average growth velocity is predicted to be 0.5～0.7μm/min. The equality of silicon nanowires with nano Au particles is better than those with nano Pt particles. The reaction mechanism of preparing large-area silicon nanowire arrays is analyzed as the result of the deoxidization of silver ion and the removal of the oxidized silicon solution by reacting with HF.