Hydraulic clamping sleeves is the key part of 5axis NC machine tool, it is able to generate large elastic deformation by the hydraulic pressure and clamp rotational degree of freedom of spindle. Hydraulic clamping sleeves have important effects on machine tool positioning and machining accuracy. Clamping torque is an important parameter for the design of hydraulic clamping sleeves. To research the clamping torque of hydraulic clamping sleeves effected by sleeves thickness, pressure, gap and sleeves length. The deformation generated as it works and contact stress distribution between clamping sleeves and spindle were calculated using the finite element method. The positive pressure was obtained between clamping sleeves and spindle by the integration of contact stress outside surface of spindle, further the clamping torque was calculated according to the contact pressure. The experiment data was obtain by measuring the clamping torque by own design testing table ,and the results of finite element method was verified. The results of verification illustrate that the mean deviation of the calculating data by the finite element method relative to the experiment data is less than 4.87%, it is a reliable data. The calculating data by the finite element method can provide reference for the structure design of hydraulic clamping sleeves.