The flexure tube is a key stress part of the nozzleflapper servovalve and easy to be broken because of fatigue. Based on conducted analysis on the mechanics in theory and stress state by twoway fluidstructure coupling simulation with calculation for the flexure tube of some type of servovalve, the influence that every structure parameter of the flexure tube on stress state was carried out. The study shows that in order to reduce the stress value in the flexure tube, the outer diameter and corner radius of the thinwall part should be increased or inner diameter and large end diameter be decreased. On the basis, the optimization design method for the flexure tube which has no effect on performance of servo valve is proposed.