Civil air defense door frames can be welded on site. The production technology of steel structure civil air defense door leaf is: first assemble and weld the skeleton, and then assemble and weld it with the inner and outer panels to form. Due to the large area of the inner and outer panels of the civil air defense door, the width of the steel plate required for the inner and outer panels is not enough to connect. 5 ~ 12mm panel is connected by welding, and 2mm gap is reserved at the groove or interface. The manual welding or submerged arc welding process commonly used in connection is easy to cause deformation of the door, and there are serious defects such as slag inclusion, porosity and cracks in the weld.