Abstract: The electro-hydraulic systems are widely applied in control of many kinds of mecha-nism in wind tunnels. With the development of wind tunnel test technique, and the requirement of miniaturization of the structure, the working pressure and the control precision of the hydrau-lic servo systems need to be improved. Under this condition, the elasticity of the fluid can not be neglected. In this paper, two engineering oriented methods of measurement of the module of elas-ticity are presented, and applied to the experiment in the lab. It shows that the module of elastic-ity of the fluid is in the range of 900MPa to 1000MPa in hydraulic systems in wind tunnels. The results are used in analysis of the problem accounted in a new built model supporting mechanism in a supersonic wind tunnel. The calculation keeps accordance with the phenomenon.