Abstract: Coupling k ε turbulence model, SIMPLEC algorithm is adopted to simulate the flow field in a rotating duct with rectangular section at arbitrary speeds. Comparison between the present calculation results and the datum from available literature is made. Agreement with experimental data is good. It is shown that the present algorithm has good numerical stability and convergence. It is found at low rotation that the location of the mainstream velocity peak is moved to the pressure side, the intensity of the secondary flow is strengthened and the flow is observed to be three dimensional. With the increasing rotation speed and under the same entrance conditions, the opposite phenomenon appears and the flow leads to two dimensional.