A chair arm is rotatably folded and assembly-free, which is applicable for a new type folding chair, said chair arm comprising a back panel pin, an arm, a fixation for the pin, and a connection screw. The back panel and the arm are connected through the screw via a screw hole formed on the top end of the arm with said screw hole being a rotation center. The pin is fixed on a side of the back panel, the fixation for the pin comprises an arm housing, an unlocking hand knob, a locking member, an elastic member and a fixation screw, a slide slot is formed on the inner side of the arm housing facing the back panel, when the back panel is rotated, the screw hole on the top end of the arm functions as a rotation center, the pin on the back panel contacts the locking member through the guide slot on the arm, the locking member slides inside the guide slot on the arm as acted on by the pin, when the pin enters into the inner side of the locking member, the lock member is reset as acted on by the elastic member, and the locking member and the guide slot on the arm form a locking hole for locking the back panel pin.