Typhoon Winnie and Wipha were selected as examples of enhanced and weakened typhoon for numerical simulation,then the large-scale field and vorticity budget field were diagnosed and analyzed by using the model results. Results show that in Winnie process, the high trough on the northwest side of typhoon tends to present northwest-southeast trend, and the intensity of South Asia high is weak, which has little blocking effect on the eastward movement of high trough. The main reason for Winnie's early stage of denaturation is that frontal system and baroclinic property play a key role. After the degeneration completes, Winnie strengthens under the joint action of baroclinic property, high-rise divergence and vorticity advection.The Wipha process is affected by the strong South Asia high and the subtropical high. The northwest high trough is stable and has a northeast-southwest trend. The cold air intrusion is not obvious, and the area and strength of the baroclinic zone are limited. In addition, neither the divergence field nor the vorticity flat flow field can provide favorable environment for the enhancement of the Wipha.