Given that Coriolis flowmeters measure flow based on vibration principles, external vibrations can significantly interfere with their measurement accuracy. The impact of external vibrations on Coriolis flowmeters was systematically investigated. A finite element simulation model was built in a bidirectional fluid-structure interaction approach, followed by series of simulation analyses. Based on the simulation results, a mathematical model was developed to describe the relationship between external vibration and measurement error, and then vibration thresholds for various accuracy requirements were calculated. The results show that the model effectively quantifies the correlation between key parameters of external vibration, such as frequency and amplitude, and measurement errors. This provides theoretical support for a deeper understanding of the impact mechanism of external vibrations on the accuracy of flowmeters. The model can be used to assess the effect of external vibrations on the performance of flowmeters under different operating conditions, offering scientific guidance for on-site installation and usage.