Abstract: Based on the Cauchy-Helmholtz theorem and the Smagorinsky model,a second-order dynamic sub-grid-scale (SGS) model with two dynamic coefficents is proposed,in which the sub-grid scale stress is the function of both strain-rate tensor and rotation-rate tensor.The velocity and pressure fields are calculated by using the simplec algorithm and the finite difference approximation to discretice the governing equations.Compatison between computational and experimental results of velovity and pressure fields in a curving conduit is conducted.The computarional results are in good agreement with the experimental ones.