An external airbag structure for a vehicle includes an airbag cushion disposed to develop toward a front side of a bumper from a folded state, a vent hole formed at the airbag cushion, and a variable vent cover attached to the airbag cushion to block the vent hole, wherein the variable vent cover includes a material having a heat-resisting property which is melted and torn by a temperature and/or a pressure of an internal expansion gas of the airbag cushion on expansion of the airbag cushion. The vent hole is opened to perform an effective cushion action as the airbag cushion is developed.