The utility model relates to an automatic gearbox technical field provides an automatic derailleur selects actuating mechanism that shifts, including selector shaft, install selection shelves shift fork and the first driven toothed sector that shifts on selector shaft, automatic derailleur selects actuating mechanism that shifts still include with the first driven toothed sector engaged with second of the shifting driven toothed sector that shifts, automatic derailleur selects actuating mechanism that shifts still keeps off with the selection with brushless direct current torque motor including shifting and uses brushless direct current torque motor, wherein, shift with brushless direct current torque motor and the second driven toothed sector fixed connection that shifts, the selection keeps off with brushless direct current torque motor and selection shelves shift fork fixed connection, the operation thereby realization automatic gearbox's selection is shifted, high reliability, overload factor is big, but direct drive load, whole actuating mechanism's the machine design degree of difficulty has been reduced, and control is accurate.