Abstract: The thread guide mechanism of rotary blades belongs to the one of changing direction by relay,(i.e.,) the back and forth motion of yarns is guided by two rotary blades rotating in the opposite directions and as soon as the yarns travel to the end of the stroke,they change their directions through exchanging positions on the rotary blades.The thread guiding mechanism of several kinds of imported high speed take-up machines and precise winders is analyzed,and the design method of this kind of thread guide mechanism is proposed for the first time.General formulas for this design are derived and the design theory has been proven correct by illustrative examples.This design method and formulas may be used for reference in designing the same kind of mechanism.