This paper aims at analyzing the discharge characteristics of servo-valve spool valve under the conditions of laminar and turbulent flow, and establishing a general mathematical model for the orifice flow. The discharge characteristics of spool valve orifices are simulated by the CFD method and a formula for discharge coefficient C-d and Reynolds number R is derived. Based on the formula and the submerged orifice flow equation, a general orifice flow mathematical model adapting to meet both turbulent and laminar flow is proposed. Finally, a flapper-nozzle mechanism is designed and machined by the protection part machining method to simulate the spool valve orifice. Flow experiments of the flapper-nozzle mechanism and an actual spool valve have been carried out, respectively. The flow model is verified through comparing the experimental results with the numerical simulation results. (C) 2011 Elsevier Ltd. All rights reserved.