A side curtain airbag for a vehicle, comprising: a serial main chamber that inflates and deploys along an interior side surface of the vehicle; a protruding chamber disposed at a front side of the main chamber to further protrude toward an interior of the vehicle relative to the main chamber; and a cutting line arranged between the main chamber and the protruding chamber to partially separate the protruding chamber from the main chamber, wherein the protruding chamber overlaps with a portion of the main chamber in a non-inflated and unfolded state of the airbag, a foremost chamber extending from a front end of the main chamber toward the front side of the vehicle to be downwardly deployed from a front pillar of the vehicle, wherein the protruding chamber is disposed between the main chamber and the foremost chamber 150), wherein the protruding chamber is defined by a protruding chamber wall, the protruding chamber wall comprises a vertical wall protruding upwardly from a lower portion of the airbag; and a transverse wall extending from a top end of the vertical wall toward the front side of the vehicle and spaced from the upper end of the curtain airbag by a predetermined distance, and the cutting line is formed in a non-inflation area (A1, A2, A3) around the vertical wall and the transverse wall, characterized in that a first upper point and a second upper point in a non-inflation area above the transverse wall are coupled to each other by a first connecting means after an upper portion above the transverse wall is folded through at least one folding line (F1, F2), and a first lower point in a non-inflation area below the main chamber and a second lower point in a non-inflation area below the protruding chamber are coupled to each other by a second connecting means after the protruding chamber and the main chamber overlap each other. a serial main chamber that inflates and deploys along an interior side surface of the vehicle; a protruding chamber disposed at a front side of the main chamber to further protrude toward an interior of the vehicle relative to the main chamber; and a cutting line arranged between the main chamber and the protruding chamber to partially separate the protruding chamber from the main chamber, wherein the protruding chamber overlaps with a portion of the main chamber in a non-inflated and unfolded state of the airbag, a foremost chamber extending from a front end of the main chamber toward the front side of the vehicle to be downwardly deployed from a front pillar of the vehicle, wherein the protruding chamber is disposed between the main chamber and the foremost chamber 150), wherein the protruding chamber is defined by a protruding chamber wall, the protruding chamber wall comprises a vertical wall protruding upwardly from a lower portion of the airbag; and a transverse wall extending from a top end of the vertical wall toward the front side of the vehicle and spaced from the upper end of the curtain airbag by a predetermined distance, and the cutting line is formed in a non-inflation area (A1, A2, A3) around the vertical wall and the transverse wall, characterized in that a first upper point and a second upper point in a non-inflation area above the transverse wall are coupled to each other by a first connecting means after an upper portion above the transverse wall is folded through at least one folding line (F1, F2), and a first lower point in a non-inflation area below the main chamber and a second lower point in a non-inflation area below the protruding chamber are coupled to each other by a second connecting means after the protruding chamber and the main chamber overlap each other.