Abstract: A hot extrusion die for a special-shaped square pipe includes a die cavity sleeve with a special-shaped cavity. A hot extrusion mandrel is arranged in the die cavity sleeve. An area between the die cavity sleeve and the hot extrusion mandrel forms a die cavity hole. A first extrusion diversion hole and a second extrusion diversion hole are arranged below the die cavity hole. An integral centroid of the die cavity hole is located at a circle center of a radial cross section of the die cavity sleeve. Further disclosed is a hot extrusion integral forming method for a special-shaped square pipe, including: heating and expanding a blank material; heating the blank material again after expanding; performing hot extrusion on the blank material; and cooling the formed special-shaped square pipe in air to a room temperature, and inspecting surface quality and mechanical properties of the special-shaped square pipe.