A curtain airbag system of a vehicle is provided and omits a front or rear pillar area of a roof/side frame for a space for accommodating an airbag cushion. The airbag cushion is guided by a connection tether for a deployment direction to deploy the airbag cushion to a protection zone for an occupant. Additionally, the airbag cushion is folded in a zigzag form to expose the connection tether, thereby guiding the airbag cushion for the deployment direction and securing a deployment speed.