The present invention provides a positioning structure of the electrical connector comprising a housing with a slot and a plurality of terminals, at least two side arms positioned on the two side of the housing, every side arm is comprising an extension plate which assembled to the housing, a movable arm and a fixed arm, and the fixed arm has an inserting plate extending downwardly, and at least two positioning sets respectively receiving the side arms. Every positioning set comprises a straight plate and the bent plates respectively positioned on the two sides of the straight plate, a receiving chamber is formed between the bent plates for receiving the inserting plate. Thus by having the bottom portion of the straight plate of the positioning set and every bent plate welded to the circuit board in order to increase the welding area, and to restrict the side arm by every positioning set, thus not only the housing is precisely positioned and also the fine adjustment during the assembling can be implemented; therefore, the present invention provides the convenience for assembling, the stability for welding and accordingly to increase the yield.