An airbag system for a vehicle is provided. The system includes an airbag cushion that is deployed from the upper portion of a seatback to cover the head of an occupant, thereby absorbing impacts applied to the head of the occupant and preventing neck bending attributable to movement of the head of the occupant. In addition, injury to the occupant is minimized by variably adjusting the deployment timing of the airbag cushion depending on the collision direction of the vehicle.