| These years Coriolis mass flowmeter (CMF) has been growing fast, and with the most advantages, CMF has obvious superority in the field of the direct mass flow measurement. But,at the present time, because the model is excessively simplified ,the low analytic precision is caused and the measurement performances are not analyzed effectively by it. In this paper, the model of single-straight tube CMF is constructed and the performances are analyzed and the conclusion is valuable.The theoretical model is hypothesized. Considering the driver and detector masses, the vibration differential equation is derived based on force analysis of tube and fluid micro- unit body, and the fluid-solid interaction between the tube and the fluid is revealed. Because the flowing velocity of fluid in the tube is not considered stable here , the vibration differential equation is better common.Another vibration differential equation is derived by considering the flowing velocity stable. Solution of the equation is given by using the Galerkin method , and the expressions of sensitivity and fluid density-resonance frequency are given in the condition of considering lumped mass or without considering lumped mass respectively. The effects of lumped masses and fluid density on sensitivity are analyzed and the optimal allocation of the detector is obtained: if the detector mass is as double as the driver mass, the optimal allocation is 0.15L or 0.33L; if the detector and driver masses are nearly equal, the optimal allocation is 0.27L. This conclusion is more applied than 0.37L that has been given before. The effects of frequency error on fluid density measuring precision are analyzed theoretically, which should offer the theoretical basis to error control of on-line density measure .
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