To study the influence of by the screw pitch and the Stagger Distance on the spindle of flattended yarn quality， and to analyze the relationship among the transmission ratio, the screw pitch and the Stagger Distance, and to solve the problem of position conversion for different specifications of flat yarn in the production. Empirical data were obtained through repeated experiments, and the mechanism of Multi-Position Rapid Conversion was designed combining theoretical analysis, and the substantial structural transformation was implemented for the winding machine on the production line of plastic woven sack. An old winding machine could only be used by flat plastic yarn of one specification, while the new machine could be used by a variety of specifications through simple position change. The production efficiency and product quality were both significantly improved. Reasonable screw pitch and Stagger Distance were important for the quality of the spindle of the flattended yarn, and they could be effectively controlled by designing the transmission ratio to meet the requirements of different specifications of flat yarn. The practical problems could be effectively solved by the designed mechanism of Multi-Position Rapid Conversion.