The utility model discloses a prepressing system for hanging basket main trusses. The prepressing system comprises two hanging basket main trusses which are arranged symmetrically in the same plane, wherein middle vertical beams of the two hanging basket main trusses are fixedly connected through I-beams; tail part anchoring ends of the two hanging basket main trusses are fixed through a tail end fixing frame; front part anchoring ends of the two hanging basket main trusses are arranged in a front end fixing frame; two supporting I-beams are arranged on two inner sides of the front end fixing frame; the inner side of an I-beam on one side is closely contacted with the outer side of a front part anchoring end of the hanging basket main truss on a corresponding side; and a hydraulic jack is arranged between the inner side of a supporting I-beam on the other side and the outer side of a front part anchoring end of a hanging basket main truss on a corresponding side. According to the prepressing system, the hanging basket main trusses are prepressed by the hydraulic jack arranged in the front end fixing frame, the structure is simple, a long-time preparation process is not required, and the loading and unloading time is short; the system has the advantages of low cost and high accuracy; and at the same time, potential safety hazards during work can be reduced.