Thermowells were often fractured due to the impact of fluid flow with high temperature and high velocity. The large eddy simulation technique was utilized to simulate the unsteady internal pipe flow field around a specified thermowell. The force and the vibration of the thermowell induced by the unsteady flow were analysed. An improved measure, which set up an interference equipment in the front of the thermowell, was presented to suppress the vibration and reduce the force of the thermowell. The effect of the improved measure was also verified. This study would be useful to the structural optimization design for thermowells.