Abstract: To meet the requirement for the vibration test for the coming ultra large spacecraft structures, single-cabin vibration tests have to be carried out for individual substructures. This paper proposes a method to obtain the transfer function of the whole spacecraft based on the substructure vibration test data. With the mapping relations among different boundary modal shapes, the modal shape of a certain cabin with fixed ends is identified. Then, the modal parameters of the combined structure are calculated by the modal integration technique, and the transfer functions of the acceleration response of the structure are calculated, so the test response curve for the whole spacecraft can be deduced under the given acceleration test conditions. The method is verified by a dynamics simulation, and its engineering feasibility is shown.