Span self-adjusting variable amplitude system and crane

The invention discloses a span self-adjusting variable-amplitude system and a crane in the technical field of cranes, and aims to solve the problem that in the prior art, when a variable-amplitude system is assembled and connected, a user usually needs to stand on an arm frame to work, and the disassembly and assembly work of the variable-amplitude system cannot be completed on the ground. The crane jib luffing device comprises a jib and a jib luffing mechanism which are arranged on a crane, and the jib is located on one side of the jib The luffing mechanism comprises a pulling plate group, the pulling plate group comprises two first pulling plates, switching pulling plates are arranged at the two ends of each first pulling plate, a telescopic mechanism is arranged between the two switching pulling plates, balance mechanisms are movably connected to the telescopic mechanism, one balance mechanism is movably connected with the mast, and the other balance mechanism is movably connected with the top knuckle arm;