In this work, vibration characteristics of a flue gas cooler(FGC) for a heavy oil upgrading are experimentally analyzed and an effective method is proposed to reduce the vibration level. Firstly, the vibration under the operation condition of the FGC is measured and analyzed to identify the generation phenomena of vibration. And the displacement of the outer wall of the FGC is also analyzed to identify dominant frequencies of vibration. Secondly, an effective design to reduce the vibration is suggested by using the modal analysis. Consequently an improved design of the FGC gas cooler, which has lower vibration level, is obtained and then verified though the analysis and test.