Abstract: Resonant Coriolis mass flowmeter (CMF) measures liquid mass flux via the Coriolis theory of the measurement tubes resonant vibration. Actually the external coupling and the internal coupling vibration are widely existent, the operating stability and the measurement precision are directly influenced. The external coupling vibration was resolved by increasing the straight pipelines or strengthening the sensor fixure, but the internal coupling vibration is absence of flawless theoretical guidance and solution. The internal coupling vibration phenomenon and the influence to measurement precision of the sensor were put forward on the basis of the Coriolis mass flowmeter operating mechanism, the comparison experiments of the CMFs with internal coupling vibration and without internal coupling vibration were made by using Polytec laser doppler vibrometer, it was revealed that the internal coupling vibration is tantamount to the additive weight on the main vibration, the additive phase difference was induced. For the special CMF, the additive weight is mostly steady, but the Coriolis force increases with the fluid flux, therefore the influence of internal vibration decreases with the increased fluid flux and the measurement error is decreased.