Seasonal variation in the circulation of the East China Sea is discussed in this talk by analyzing the Finite-difference Galerkin function model results given by Junge et al (2001). In the paper by Jung et al (2001) the monthly depth-mean flow fields in the Yellow Sea and the East China Sea were presented. Vertical structures in the circulation of the East China Sea is here presented with particular attention on the formation of Cheju Cyclonic Gyre and its geophysical implication to the mud-patch distribution at the sea bottom.