Abstract: Boundary effect of a fixture is the main factor that affects the precision in a vibration test. In environment engineering, the field vibration environment can be simulated by a base movement excited by a shaker under the assumption that the reaction between the test item and the fixture can be neglected. Therefore, the validity of the test depends on how far the test boundary can be considered as with infinite impedance connection. A new method is presented to analyze the boundary effects of the fixture based on dynamic substructure analysis. A numerical simulation validates the proposed method.