Abstract: To be able to construct the expected suture stitch during the process of unilateral suture, this article focuses on design and planning the relationships among the action on each part of the mechanism. By analyzing the general relationgship between the rotation of mechanism and the displacement of the needle bar, the expression of phase difference about crank angle can be determined. While the article also uses simulation software to analyse the displacement of the mechanism.Acording to the location of the each part of the mechanism at some special moments in the simulation result, the relationships among the action on each part of the mechanism can be reflected. Simulation results demonstrate the action planing which are reasonable and efficient.，and afford a theoretical basis for debugging and construct the expected suture stitch during the process.

Key words: single edge sewing, stitch, mechanism motion, planning, analysis of displacement