Abstract: Stability design of inter tank under the seismic condition is one of the core technologies for design of large-scale liquefied natural gas (LNG) tank. Seismic parameters and inter tank characteristic dimensions of tank in a domestic LNG project are taken as an example to analyze stability of inter tanks in the seismic condition under the hypothesis of no anchoring belt in accordance with base shear force calculation, horizontal sliding checking, overturning moment calculation, inner tank stability judgment and other relevant formula in the seismiccondition given by relevant international standards. The results show that the inter tank will be subject to vertical uplift if no effective measures are used. Comparison between two common international protection measures indicates that the method of increasing annular plate size of inter tank bottom edge has more advantages than that of installing an anchoring belt in the construction convenience, materials conservation and other aspects.