The invention relates to a skateboard pneumatic assembling device, which comprises a rack, a positioning seat arranged on a tooling platform of the rack, a skateboard upper pressing mechanism, a cover plate compression mechanism, a boarding compression mechanism and a control system, wherein a workpiece position to be assembled is arranged in the middle of the tooling platform, and the positioning seat, the skateboard upper pressing mechanism, the cover plate compression mechanism and the boarding compression mechanism are respectively positioned at the front side, the left side, the right side or the back side of the tooling platform according to the position of the positioned or compressed workpiece; and the control system controls compression cylinders of the compression mechanisms to be compressed or released, and thus the compression positioning of oil tank components needing to be assembled is realized. The skateboard pneumatic assembling device is flexible, is fast to compress, and is convenient to operate, the tooling of an oil tank is semi-automatic, the efficiency is improved, the labor intensity and the manufacturing cost are reduced, the stability of the tooling accuracy and the product quality is ensured; and the assembly gap of the oil tank is very small, so that welding slag are avoided being splashed into the oil tank, and thus the time of cleaning the inside of the oil tank in the following step can be shortened.