An electrical plug connector includes an insulated housing, contact terminals held in the insulated housing, an outer shell covering the insulated housing, and hook members. First buckle structures are at side arms at two sides of the insulated housing. Each of the hook members includes a second buckle structure mating with the corresponding first buckle structure. The buckle structures are of crescent shapes and mated with each other. When the press portion of the hook member is pressed by an excessive force, the first/second buckle structure stops the second/first buckle structure to prevent the elastic arm of the hook member from deforming. When the elastic arm is bounced back excessively, the first/second buckle structure stops the second/first buckle structure to prevent the hook member from detaching off the side arm.