The utility model discloses a cold-bending square tube for a tower cap of a tower crane, which is used for solving the technical problem of small sectional inertial moment of the existing cold-bending square tube. The cold-bending square tube comprises a whole stainless steel plate which is cold-bent into the shape of a hollow square, high-frequency weld joints (5) are arranged at butt joint interfaces of the stainless steel plate, four angles of a tube wall outer profile (1) with a hollow square-shaped section are outer circular arcs (2), the radius of the outer circular arcs (2) is 20mm, the four angles of a tube wall inner hole (3) with a hollow square-shaped section are inner circular arcs (4), and the radius of the inner circular arcs (4) is 10mm. The cold-bending square tube disclosed by the utility model can be widely applied in the aspects of tower cranes, process steel structures and the like, the product variety of the cold-bending square tube is increased, and the range of application of the cold-bending square and rectangular tube is expanded.