The invention discloses a double layer overpressure resistant cabin body of a great depth underwater vehicle and a molding method thereof. The cabin body includes an inner shell, an outer shell, a backing plate and an insulating coating; the inner shell is in a structural form that flanges on the two ends and the middle part includes a cylinder and outer ring ribs; the flanges on the two ends canbe connected to other sections; the ring ribs of the inner shell are in equidistant distribution; the wall thickness of the inner shell close to girth weld are gradually increased, so that the increasing of the integral intensity and stiffness of the structure can be achieved, and weld positions can be ensured that the subjected stress is small when being subjected to external pressure; the outershell adopts a thin wall cylinder shell and is formed by thin-wall plates through roll welding, and the welding seam is longitudinal; and the inner shell and the outer shell of the cabin body are in connection through the abutting joint of the girth weld, and the small cavity structure on the back of the girth weld can guarantee that the structural form of butt welding can be realized easily. Thecabin body is high in underwater overpressure resistance, good in overpressure resistant stability, light in weight, high in specific strength, good in impact resistance, long in seawater corrosion resistance duration and long in service life.