Abstract:The maintenance process of typhoon Winnie (1997) after landfall was reappeared by using the MM5 model. The numerical simulations cover the entire process inclu ding initial weakening, extratropical transition and redeveloping. The adiabatic and diabatic effect on the local change of potential vorticity (PV) at lower tr oposphere was analyzed, during the entire process using Ertel potential vorticit y budget equation on isentropic surface. The results show that the PV increases in the west and north of tropical cyclone at lower troposphere and the location of core is not the same to the typhoon. Because of the existence of friction a nd diabatic heating, the PV changed at lower troposphere. The local change is mainly decided by the horizontal advection ofPV (conservation term), vertical advection of PV, vertical differential of heati ng (non conservation terms). With the happening of extratropical transition, th e PV at lower troposphere changed further and the positive effect of diabatic te rms especially vertical differential of heating on the local increase of PV domi nated.