Considering that the length and thickness of thin-walled sleeve, the depth of ring groove of thin-walled sleeve and the magnitude of hydraulic pressure on thin-walled sleeve all affect the deformation, positioning accuracy of workpiece and clamping force on workpiece, ANSYS platform is used to model the hydraulic expansion positioning fixture with finite element, and the law of influences of these parameters on the workpiece are also analyzed.By optimizing these parameters in structural design, optimized parameters were obtained to get a better sealing performance for the hydraulic oil, smaller deformation and stress of workpieces and thin-walled sleeve, and good clamping force.The results show that the deformation of the workpiece decreases from 1.5 μm to 0.9 μm, the maximum stress of the thinwalled sleeve decreases from 292.88 MPa to 282.34 MPa, the radial deformation of the joint surface of the two ends of the thinwalled sleeve decreases from 11.8 μm to 8.6 μm, and the clamping moment decreases from 124.36 N·m to 67.33 N·m.