The invention relates to an electric connector at a free end, which mainly comprises a plug, as well as a head casing, a clamp spring and a clamping cap which are arranged on the plug, wherein, the head casing is locked with the clamping cap by a clamp spring; a plurality of bayonet pins are mounted on the inner wall of the clamping cap; a plurality of grooves corresponding to the positions of the bayonet pins are formed on the external circle of the supporting panel of the head casing; the cross section of the groove is larger than the cross section of the bayonet pin; the head casing is rotated to lead the grooves to correspond to the bayonet pins, so that the head casing is mounted in the clamping cap or withdrawn out of the clamping cap. The invention has the advantages of simple structure, convenient assembly and disassembly, and convenient test and maintenance, thereby improving the finished product ratio of products.