Abstract: Aiming at the technical challenges of precise measurement of mass flow of large-diameter liquefied natural gas （LNG）, based on the bidirectional fluid-structure coupling numerical simulation method, this paper conducts a study on the measurement performance of the double straight-tube Coriolis mass flowmeter under LNG working medium and verifies it through experimental data. The research results show that the prediction results of the constructed bidirectional fluid-structure coupling numerical simulation method are in good agreement with the experimental data, ensuring the accuracy of the numerical calculation. The research further reveals the coupling influence mechanism of the unique physical properties of LNG on the dynamic behavior of the measuring tube: The low density of LNG weakens the additional mass effect of the fluid, making the reduction in its wet-mode natural frequency significantly lower than that of the water working medium. The stable amplitude of the water working medium is 80% of that of the LNG working medium, while the low viscosity characteristic of LNG proifies the time for the vibration to reach a stable state. Although the time delay at the detection point maintains a linear relationship with the mass flow rate, the low density of LNG weakens the Coriolis force. Coupled with the increased driving difficulty caused by low temperature and high stiffness, the time delay difference is significantly reduced, by approximately 15% to 22% compared to water-based working fluids. Moreover, the time delay difference expands with the increase in flow rate, indicating that the precise measurement of small time delays （μs level） is the core difficulty in the application of LNG. To this end, it is proposed to improve the sensitivity and signal-to-noise ratio by optimizing the structure of the measuring tube and enhancing the excitation force. The research results provide theoretical basis and data support for the design optimization and engineering application of large-diameter low-temperature Coriolis flowmeters.