parallel machine vice is a type of general fixture, it has some defect for positioning for machining work piece need to be completely fixed. We designed a type of assistant positioning device for parallel machine vice to ensure complete positioning of work piece. The device can be easily and conveniently installed on the guide rail of a parallel machine vice, which keeps the generality of the machine vice and improves its performance. It features new structural design, easy to be processed, easy for use and optimized working efficiency and can be classified as a type of assistant positioning device of machine fixture with integral advantages economical efficiency and practicability.