Abstract: The flow induced vibration (FIV) tests of heat transfer helical tube bundle of a liquid-reactor were carried out. Two parts were included: Calculation and test on vibration characteristics in air and water of structure；FIV test in steady-state and transient condition. The results show that the larger internal flow velocity becomes, the higher pressure drop of bundle is, and the up restraint positions are weak. The dynamic buckling of bundle does not occur during steady-state operation, the tubes are not contacted, and the fatigue evaluation was done according to ASME code and the structure is founded to satisfy the ASME code requirements. The transient maximum vibration displacements and strains are larger 2 orders than steady-state values.