A longitudinal-slide door controlling mechanism is provided to improve door controlling for large vehicles, such as buses. The door controlling mechanism is designed to longitudinal-slide to save space-occupied by the door and enhance safety. The mechanism includes a track, a slider group, a flexible transmission group, and a drive element. The flexible transmission group is used to drive the slider group to move along the track. And the track is attached to the bus body. Therefore the bus door is driven to longitudinal-slide along the bus body. The space-occupied caused by the conventional rotary door is saved. Also, the passerby struck by the door during opening would be eliminated.