This paper presents the sensitivity analysis of a sample hydraulic servo valve. The sensitivity of the flow-current curve with respect to variations of geometrical and functional parameters is evaluated. This analysis is done by use of a model which simulates the valve behavior in terms of geometrical parameters and properties of components. With attention to multiplicity of the valve components and the complexity of the system, the more effective parameters have been studied more precisely. Deviation of “flow gain” And “saturation flow” -which are the main characteristics of the valve behavior- from their nominal values in the flow-current curve, is the criterion for the valve sensitivity assessment. The curve of characteristic variations versus parameter variations has been plotted. The evaluations indicated that all of the sensitivity curves are linear in the limited intervals. Also between the evaluated parameters, “nozzle-flapper equilibrium distance”, “orifice diameter” and “stiffness of spool spring” have more sensitivity effect on the valve performance, respectively.