The utility model provides a preharvest treatment device of a maize harvesting machine. The preharvest treatment device of the maize harvesting machine can reduce weight. A pretreatment frame is composed of a left longitudinal plate shape connecting frame, a right longitudinal plate shape connecting frame, a transverse frame and a connecting component. The left longitudinal plate shape connecting frame and the right longitudinal plate shape connecting frame form a pair, and the rear end portions of the left longitudinal plate shape connecting frame and the right longitudinal plate shape connecting frame are freely connected with a driving machine body in a rotating mode. The transverse frame is arranged in the transverse direction of the driving machine body and connected with the lower portions of the front end sides of the left longitudinal plate shape connecting frame and the right longitudinal plate shape connecting frame. Transverse two ends of the transverse frame protrude towards the transverse outer side of the transverse frame from the left longitudinal plate shape connecting frame and the right longitudinal plate shape connecting frame. The connecting component stretches from the transverse frame towards the front of the drive machine body, and the stretching end portion of the connecting component is located below a transverse conveying bottom plate when the stretching end portion of the connecting component is connected with a supporting frame which is arranged in the transverse direction of the driving machine body and supports a plurality of harvesting devices.