The invention discloses a supporting leg swinging and steering mechanism for a milling-planing machine.The mechanism comprises a milling-planing machine frame, a swinging rod, a steering rod, a first guide rod and a second guide rod; a supporting leg of the milling-planing machine comprises a supporting leg outer sleeve and a supporting leg inner sleeve, and the supporting leg outer sleeve is arranged on the supporting leg inner sleeve which can rotate relative to the supporting leg outer sleeve in a sleeving mode; one end of the swinging rod is hinged to the milling-planing machine frame, and the other end of the swinging rod is fixedly connected with the supporting leg outer sleeve; one end of the second guide rod is hinged to the milling-planing machine frame, the other end of the second guide rod is hinged to one end of the first guide rod, the other end of the first guide rod is hinged to one end of the steering rod, and the other end of the steering rod is connected with the supporting leg inner sleeve.By means of the supporting leg swinging and steering mechanism for the milling-planing machine, the cost is reduced, and control operation of swinging and steering is convenient.