The present paper is concerned with characteristics of flow structures of typhoons, and the double variational method is applied. First, the typhoon flow field is decomposed into two parts: the maximum asymmetric vortex and irrotational environmental flow field. Then the maximum asymmetric vortex is also decomposed into two parts: the maximum symmetric vortex and β-gyres. Finally, typhoon Pearl(2006) is simulated by WRF model(weather research and forcasting model), and flow fields at various times at 500hPa are decomposed using the above method. It turns out that the decomposed flow fields are useful for researches on motion and track prediction of typhoons.