A vehicle antenna mounting apparatus is disclosed, which includes: a base member mounted on an outer surface of a vehicle panel and covering an mounting hole formed in the outer surface; a screw shaft extending from a lower surface of the base member and passing through the mounting hole; and a fastening member having a support portion supported on the base member, and a plurality of elastic deformation portions extending from the support portion and provided with a locking portion at a lower end of the elastic deformation portions; a deformation guide member which is coupled to an outer surface of the screw shaft; and a tightening nut fastened to the screw shaft for moving and supporting the deformation guide member. The deformation guide member presses the elastic deformation portions in the radial direction of the screw shaft as the deformation guide member moves toward the base member.