A torsion beam of a coupled torsion beam axle may include an external beam having a first cross-section in which an external protrusion of a middle end portion of the external beam is formed to protrude toward upward in a longitudinal direction of the external beam, and external skirt portions are vertically extended along the longitudinal direction at both end portions of the external protrusion; and an internal beam having a second cross-section in which an internal protrusion of a middle end portion in the internal beam is inserted into the external beam to face the external protrusion of the external beam, and internal skirt portions are extended in a vertical direction at both end portions of the internal protrusion, and each external surface of the internal skirt portions and each internal surface of the external skirt portions are surface-bonded in a mutually matched state. A gap is formed between an external surface of the internal protrusion and an internal surface of the external protrusion to form a closed cross-section.