The present application provide a battery pack and a cooling system thereof. The cooling system includes: a collecting tube, including a body portion having a cooling flow channel; a cooling tube which is provided with a collecting tube at both ends along the axial direction and is in communication with the cooling flow channel of the collecting tube; the body portion is further provided with a mounting hole, a limiting boss is arranged inside the mounting hole, and abuts against the cooling tube along the axial direction. By disposing the limiting boss in the mounting hole, the cooling tube abuts against the limiting boss, which function to limit the cooling tube in the width direction, realize the connection between the cooling tube and the two collecting tubes, and limit the depth of the cooling tube entering into the mounting hole through the limiting boss.