A plug connector is for connecting to a receptacle connector. The receptacle connector comprises two resilient plates. The plug connector has an insulating housing and a metal shell. The insulating housing includes a tongue portion and a base portion for accommodating and connecting the terminals. The metal shell has a top plate, bottom plate, and two side plates. Multiple recesses, protrusions or elongated recesses are selectively formed on at least one of the top plate, the bottom plate for connecting the resilient plates. These can avoid electromagnetic interference, dusts or any external substances from attaching to the insulating house and also ensure a high quality of the insertion force and the extraction force after frequent uses.