The utility model discloses a supporting leg swing mechanism, a supporting leg and an engineering machine. The supporting leg swing mechanism is used for driving the supporting leg to be opened and retracted, the supporting leg is hinged to an underframe through an articulated shaft, a driving device is arranged on the underframe or the supporting leg, and a driven wheel is correspondingly arranged on the supporting leg or the underframe. The driving device is connected with a driving wheel and drives the driving wheel. The axial line of the driven wheel is overlapped with that of the articulated shaft. A first flat rope and a second flat rope are both connected with the driving wheel and the driven wheel, and the driving wheel drives the driven wheel to rotate through the flat ropes to enable the supporting leg to have a retracting position and a fully-opening position. At the retracting position, the driving wheel can drive the driven wheel to rotate in the first direction through the first flat rope; at the fully-opening position, the driving wheel can drive the driven wheel to rotate in the second direction through the second flat rope; the first direction is opposite to the second direction. The supporting leg swing mechanism is small in occupied space, flexible in layout and capable of locking the supporting leg at proper positions.