The invention provides a double-spindle turn-milling composite machining machine tool for an aero-engine casing, which is characterized in that a horizontal shaft ram for transversely machining the casing is arranged on the outside of a machine tool body through a cross sliding table, and a main sliding table is arranged below the machine tool body. Through the arrangement, the inside molded surface and the outside molded surface of the aero-engine casing can be subjected to turning-milling composite machining in vertical and horizontal directions at the same time, which is conducive to improving the machining precision and the work efficiency.