Abstract: [Objectives] With the beginning of the application of sandwich composite materials in ship structure, in order to ensure the strength characteristics of the structure, bolt connection is usually used between the sandwich composite structure and the steel main hull, but due to the local stress concentration around the hole and the boundary effect of the connection position, the bolt connection position is usually the most dangerous position of the structure, strength and fatigue checks are required. [Methods] For a full-scale steel-sandwich composite plate frame structure, the strength characteristics of the plate frame under 0.1MPa uniform load were studied by test method and finite element method. [Results] By comparing the measured results of the test and the calculated results of the finite element method, it was found that the error between the calculated results of the finite element method and the measured results of the test is less than 10%, and the finite element method has a high calculation accuracy. [Conclusions] Therefore, based on the finite element method, fatigue tests of two equivalent local joints were designed by means of structural stress equivalence, and the fatigue life of the steel-sandwich composite structure was checked and verified. It was found that the fatigue life of the plate structure under the design load met the design requirement of 5 million times.