Abstract: Ground barrier systems are widely used for vibration control in geotechnical engineering. They usually impede and change wave propagating in ground to reduce or eliminate the vibration in protected zones. However, some barrier systems are not effective. Observations show that in some cases, the vibrations in protected zones can be amplified. This paper presents a theoretical analysis of such unusual phenomenon. In the analysis, the barrier system is assumed to be an infinite elastic plate embedded in elastic soils. The dynamic response of the impeded plate under an incident P wave is examined. The paper proposes the resonant frequency of the barrier soil system and the induced source of vibration,and gives a simple equation to calculate the resonant frequency and applied it to analyze the test results presented by Barkan(1948). Results show that the unusual phenomenon of the vibration amplification in protected zone can be explained by the new concept.