The invention discloses a combined IMO A-type cargo containment system for an ultra-low-temperature liquefied gas transport ship. The combined IMO A-type cargo containment system comprises a bilayer hull and an IMO A-type standard liquid cargo tank, and a low-temperature-resistant metal structural member and a supporting cushion block are arranged between the bilayer hull and the liquid cargo tank for supporting; an insulating layer is fixed on one side close to the bilayer hull, a fully-sealed thin film layer made from an invar material is arranged on the surface of the insulating layer, and the insulating layer and the fully-sealed thin film layer are hermetically connected by a stainless steel connecting member; the IMO A-type standard liquid cargo tank serves as a main barrier layer, the fully-sealed thin film layer and the insulating layer are combined together through the stainless steel connecting member to form a secondary barrier layer which is not complete, and sliding is allowed between the secondary barrier layer and the bilayer hull, so that the secondary barrier layer cannot be torn along with deformation of the bilayer hull. Consumption of ultra-low-temperature steel which is expensive is lowered, and building cost is lowered; capability of the secondary barrier layer of the cargo containment system in approaching for direct inspection and maintenance is realized.