The utility model provides a semitrailer supporting leg structure and a semitrailer. The semitrailer supporting leg structure is applied to a semitrailer which is provided with a frame and a ladder stand which can rotate around the tail end of the frame; the semitrailer supporting leg structure comprises a connecting piece, a supporting leg fixing seat and a supporting leg, wherein the supporting leg fixing seat is fixed below the tail end of the frame; the supporting leg comprises an upper end and a lower end; the upper end of the supporting leg is pivotally connected with the supporting leg fixing seat; and two ends of the connecting piece are pivotally connected with the supporting leg and the ladder stand, so that the supporting leg can be correspondingly located in the folding position and the laying-down position along with the folding and laying-down of the ladder stand. Manual independent operation is not required, the manpower resources are saved, and the potential safety hazard caused by the condition that the supporting leg is not used by a user is eliminated.