The invention provides a variable wheel base unmanned aerial vehicle mechanism with a fire-extinguishing launcher. The unmanned aerial vehicle mechanism comprises a transmission assembly, an engine arm assembly, a launching assembly and a wing assembly, wherein the engine arm assembly comprises a curved bar, an upper joint, a carbon tube, a connecting rod, a lower joint, a Y-shaped connecting rod and a round nut; the curved bar, the upper joint, the carbon tube, the connecting rod, the lower joint and the Y-shaped connecting rod form a parallelogram; and the height of the parallelogram is changed under drive of external force, so that the wings are driven to always swing up and down parallel to the horizontal plane.