The utility model relates to a jib crane undersetting, it belongs to hoisting machinery technical field. The utility model discloses an upper cover plate, lower fagging in apron, seat circle, annular backup pad, outside gusset, adapter sleeve, inboard gusset and the profile modeling, the seat circle is fixed on the upper cover plate, the last lower extreme of annular backup pad, outside gusset and inboard gusset respectively with upper cover plate and cover connection down, four ends of lapping under with at the upper cover plate are fixed to the adapter sleeve, the fagging lies in upper cover plate and the neat centre of lower cover in the profile modeling, the fagging is connected with annular backup pad, outside gusset and adapter sleeve in proper order in this profile modeling. The utility model discloses it is reasonable to construct, and occupation space is little, compact structure, and be convenient for installation and dismantlement, the transportation is convenient, can repeat recycle.