1. A cable management arm, comprising:a support arm, having a connecting portion disposed at both ends of the support arm separately, and at least one chute extended in a direction along the support arm; and
at least one cable management box, having a retaining portion disposed on a side of the cable management box, and movably installed in the chute, and the cable management box including a main body and a cover, and the main body having a cross-section substantially being a U-shaped structure, and a first pivoting portion and a latching portion disposed at two end portions of an opening of the main body respectively, and the cover having a second pivoting portion configured to be corresponsive to the first pivoting portion for pivotally coupling the cover to the main body to cover the opening of the main body, and a locking means for adjusting the position of the cable management box with respect to the support arm all the time,
wherein the locking means has at least one protrusion disposed at the external periphery of the second pivoting portion and corresponsive to the support arm, and a locking effect is achieved after the protrusion and the support arm interfere with each other,
wherein the protrusion is disposed at a position when the cover is closed to 0 degree, and the locking effect is achieved after the cover is closed.