The utility model discloses a mechanical type CVT derailleur variable transmission mechanism belongs to the derailleur field. The utility model discloses a variable transmission mechanism, which comprises driving turntables, from the runner disc, transition wheel subassembly, cross ferryboat support and actuating mechanism, it is main, from the coaxial setting of runner disc, it is main, the inboard of following the runner disc is equipped with half ball grooves of relative setting respectively, transition wheel unit mount is on crossing the ferryboat support, and lie in the cavity that two and half ball grooves constitute, actuating mechanism is connected with the transmission of mistake ferryboat support, transition wheel subassembly still has can automatically regulated transition wheel subassembly and main, automatic loading system from contact force between the runner disc. The utility model discloses a variable transmission mechanism, simple structure, design benefit for each main part and gearbox the stress are even reasonable, make the structure compacter, and variable transmission mechanism can realize stable follow -up pressure according to the real work condition of derailleur, and the operation is more stable, power loss when having reduced the transmission.