Abstract: Tropical cyclone motion is simulated numerically with a quasi-geostrophic baroclinic model. The flow field of tropical cyclone is decomposed into its axisymmetric and asymmetric components. The relation between the ventilation flow vector in asymmetric flow field and the motion vector of tropical cyclone is investigated. The results of numerical experiments indicate:(1) There are both large-scale beta gyres and small-scale gyres in the asymmetric flow field. (2) The interaction of the small-scale gyres with the large-scale beta gyres leads to the oscillation of translation speed and the vacillation of translation direction for tropical cyclone. (3) The large deviation between the ventilation flow vector calculated applying Fiorino and Elsberry' s method and the motion vector of tropical cyclone exists.(4)The correlation between the ventilation flow vector calculated applying the improved method and the motion vector of tropical cyclone is very close.