The utility model relates to an automatic adjustable air deflector for a truck and belongs to the technical field of vehicle parts. Two self-lock structures are connected symmetrically and fixedly on the upper portion of the air deflector, and two push-rod support structures are fixedly connected with the top of a cab and are movably connected with slide way cavities of the two self-lock structures. The air deflector top portion is movably connected with the front end of the top of the cab, the two air deflector bottom portions are fixedly connected with the two ends of the top of the cab respectively. An electric control unit comprises an internal circuit board and a gear adjuster, an automatic control switch and a power switch, which are arranged on the outside and is powered through a truck-loaded power supply. A sensor, two electric push rods and the electric control unit are connected. According to the air deflector, the air deflector is simple in structure, convenient to operate and safe and reliable, the height of the air deflector can be adjusted conveniently and automatically according to different work conditions of different heights of containers loaded by the truck or idling, a good resistance reduction effect is achieved, and fuel oil is saved; the height can be controlled arbitrarily, and the air deflector adaptability is increased; corrective design can be performed on account of different truck models, and the truck model application range is wide.