A gantry-movable drilling, boring and milling compound machine tool is guided by matching of typical cylinders and cylindrical sliding sleeves and adopts a stepless variable frequency speed regulation mechanism and a numerical control mode. Large-scale swing bearings are adopted for support and rotation of workbenches. In the material aspect, vertical column guide rails and cylindrical movable cutters are manufactured by structural alloy steel thick-walled seamless pipes and are subjected to grinding and hard chromium plating, and the workbenches are casted by ductile cast iron. The gantry movable drilling, boring and milling compound machine tool has the advantages that the machine tool can be used for drilling and boring and has functions of excircle, inner bore, section and curved surface turning, flat surface, inclined surface, curved surface and groove milling, thread tapping and the like, lubrication, dust prevention and durability of the guide rails are guaranteed, and long-term precision is maintained. Double gantries are movable, work efficiency can be improved by machining long and large pieces by the juxtaposed double gantries together, the large-scale rotating workbenches additionally arranged at two ends can be used as two numerical control lathes, equipment utilization rate is increased, and the gantry-movable drilling, boring and milling compound machine tool is simple in structure and can meet customer machining requirements particularly when parts are large in machining face and machining length.