The present invention provides a connector against contrary flowing for medical treatment, as to its structure, it includes a connecting seat to connect with a transmitting pipe, an insertion connecting cap fixed on the connecting seat for insertion of an external connecting terminal and a needless injection cylinder, and an elastic valve plug provided between the connecting seat and the insertion connecting cap, when the injection cylinder is pulled out of the insertion connecting cap, the elastic valve plug can impede the reverse pressure generated by the transmitting pipe (or the connecting seat), in order to avoid generating of contrary flowing of blood of a patient to reduce pain.
