The invention discloses a combined tillage machine for returning dry-land straw to the field by ploughing and rotary burying. The combined tillage machine comprises a ploughing device which comprisesa frame, the frame comprises length rods at two ends, a plurality of width rods are arranged at intervals between the two length rods, and one end of each width rod is provided with a grass twining prevention device. Furrow ploughs are arranged at the other ends of the width rods on two sides of the frame, a soil breaking plough is arranged at the other end of the width rod in the middle of the frame, supporting frames are symmetrically arranged on the length rod at one end of the frame, depth-limiting wheel mechanisms are mounted on the supporting frames, and the length rod at the other end of the frame is connected with one end of a rotary burying platform of a rotary burying device. A rotary burying cutter roller is arranged between bearing fixing frames and spirally provided with rotary blades, and an intermediate gearbox is arranged in the center of the rotary burying platform and provided with a universal joint. Compared with separate operations, the combined tillage machine hasadvantages that power consumption can be reduced, field operation can be completed in one time by a tractor, soil compaction is reduced, and labor efficiency improvement and labor cost reduction are realized.