This utility model relates to a medical auxiliary instrument, which relates to an intravenous injection device instead of the person's action. The utility model comprises an outer casing 1 covered an exterior of an injector completely, wherein a front end of the outer casing 1 is equipped with a pinhead seat 8, and a back end of the outer casing is equipped with two slipways 4 equipped with a co-operating pusher 3 connected with two or three elastic anchor ties. An intermediate section of the outer casing is equipped with a tailstock of a needle tube 7 equipped with a circular hole 6 co-operating with a socket of a syringe. A faying surface between the pusher 3 and the syringe is equipped with a clip 5. The utility model has the advantages of a simple device, a low cost, safety, pushing the injector automatically, pushing the soup homogeneously, relieving a venous transfusion's pain, reducing the medical staff's labor intensity, improving the medical staff's availability.