In order to research the rules of the influence on the performances of helical rotary cylinder by the thread parameters of spiral pair to obtain the optimal parameters of the thread, the three dimensional (3D) entity model of double-helix pairs system composed of inner spiral ring, piston and output shaft was established based on the existing structure of helical rotary cylinder. And then, mesh was reasonably divided, boundary conditions and actual using conditions were correctly loaded in using FEM analysis ABAQUS. The rules of influence on the efficiency, output torque and other performance parameters of helical rotary cylinder by the thread angle and pitch parameters were analyzed. Moreover the thread parameters making best comprehensive performance of helical rotary cylinder were discovered. The analysis results have certain engineering guiding significance in optimizing performance of helical rotary cylinder.