A plastic bottle cap includes a plastic cap body. The bottom side of the cap body is an opening, and the inner wall of the cap body near the bottom side opening of the cap body is annularly provided with a groove. The sealing ring is installed in the groove, and one side of the sealing ring extends to the outside of the groove. The annular groove is opened around the inner ring of the bottle cap body. Two semi-circular rings are movably mounted in the annular groove, one end of the two semi-circular rings is rotatably connected by the first hinge, one end of the two semi-circular rings which far away from the first hinge is fixed with the first fixing block and the second fixing blocks respectively, and the first fixing block and the second fixing block correspond to the setting.