Abstract: This paper introduced the reformation of the pure mechanical drive system of the old style embroidery machine using servo motor and microcomputer technique with focuses on its design and execution.The original machine head was replaced with servo motor to drive the cloth frame.The basic outline data of the cam was measured and the lifelike imitation of the movement curve of the old machine was obtained by numerical-approximation methods such as difference equation and third order spline function.Then the movement curve data was converted into step-by-step time partition of the servo motor and the simulation operation of the servo motor was controlled by program controller.After reformation of the machine,the breakdown is down,precision of embroidery is up,and the efficiency is raised by 30%.This method can be used as an reference for the renovation of the old machine of the same kind.