This paper deals with the effect on orifice discharge characteristic by the round angle of electro-hydraulic servo valve spool metering edge. The machining method of spool metering edge can cause micro round angle on the edge. This paper firstly provides 3D geometry model and computational grids of spool valve where the round angle’s range is 0-10μm and orifice opening is 0-40μm. Secondly calculates the flow rate of the orifice on the constant differential pressure circumstances. The numerical analysis is performed by using the commercial code ‘‘Fluent’’, and the numerical results show the complete flow field inside the valve. The analysis result is to obtain the influence of round angle on discharge characteristic, quantitatively. An experimental result is used in this paper to evaluate and validate the numerical analysis of the valve. The aim of this analysis is to provide a designation reference of the spool valves which are important parts of servo valve.