Abstract: The TS-Comparison method is an analytic one based upon TS-diagram for determining the boundary of modified water-masses,using this method to analyse the modified water-masses in the western area of the East China Sea, the following results can be obtained; There are two modified water-masses besides the four original ones in this area.The modified regression cures with localizable property may exist only in the cold season.The modified exchange region closely related to the existence of clockwise circulation can be identified.In addition the model is presented for inspecting the increasing and decreasing variability about each modified water-mass in the area.Finally the relationship between mixed band and position of central fishing grounds is illustrated.