Abstract: Typhoon Winnie 1997 was one of the hurricanes that had extremely largest eyewall ever recorded. The diameter of Winnie's eyewall reached 370 km. Using the Penn State University/National Center for Atmospheric Research mesoscale model MM5 with 3 km grid horizontal spacing on the finest nested mesh, Winnie was successfully simulated in terms of track, intensity, eye and concentric eyewalls. The dynamic and thermal structure of concentric eyewalls was studied based on the model out put. It was found that the concentric eyewalls was asymmetric both in observatio n and simulation. Winnie's outer eyewall was associated with a maximum wind ring , a warm moist ring and a high voticity ring. The inner eyewall was associated w ith a secondary maximum wind ring and a warm moist ring. Upward motion dominated the whole layer of inner eyewall and the area above 2 km altitude of the outer eyewall. Downward motion was found inside the eye and the moat. Radial inflow ha ppened at the boundary layer of the outer eyewall and the moat, but radial outfl ow dominate the middle and upper level of the outer eyewall.