The invention relates to the technical field of discharging, and particularly relates to a full-automatic rectangular straight square tube discharging machine. The full-automatic rectangular straight square tube discharging machine comprises a machine tool main body, a sizing feeding system, a feeding frame, a positioning feeding system, a material pressing system, a motor, a belt pulley assembly, a speed reducer, a driving rod, a kick-out device assembly, a steel wire rope, a material clamping assembly, a small chain wheel, a chain, a large chain wheel, a spring, a roller, a stop, a bearing seat, a small rolling shaft, a rolling shaft and an inductor. Original manual feeding and measurement can be replaced by a numerical control system, so that a large amount of waste of operation is reduced, the effective working time is increased, and the production efficiency is improved; according to the design and manufacturing of the whole system, all components are connected and fastened by bolts, so that easily damaged positions and failure positions can be replaced in time, and the subsequent maintenance cost of the system is reduced; and centralization lubrication is adopted, and all of the components are periodically lubricated, so that the service life of the components is prolonged.