| Firstly, there is a review in this paper about some analyzing methods of T-S relationship, the analytical theories of T-S curves and fuzzy sets of studying water masses. Based on comparing and analyzing the principles, the characters, and the advantages and the disadvantages of each theories mentioned above, the method of fitting the membership function of oceanic waiter masses has been further studied. Then, two new fitting methods - straight positioning method and coordinate turning method about two water masses with vertical stratification are presented in accordance with the characteristics of T-S curve family of the oceanic water masses. Through analyzing the results of the mixing-diffusing model and the character of the water masses on both sides of the Bashi Channel during their mixing and modifying processes, the principles and formulae of relevant membership functions are given. Based on analyzing the results, according to the SCS monsoon experiment data and the SCS climatic year-averaged data, a certain characteristic curve of the T-S curve family is modified. The membership functions of oceanic Subsurface Water Mass with high salinity and Intermediate Water Mass with low salinity are simulated by using the new methods and discussed. It is indicated that they are very useful and valuable in analyzing the distributional features and mixing and modifying processes of these water masses, especially in tracing back to their sources.In this paper, the oceanic "central water masses" have also been analyzed. In fact, the so-called "central water masses" include two parts - the subtropical mode water and the thermocline water. There are reasoned discussions about their different physical and chemical characters as well as their different resources and the producing mechanism. Through the discussion about the "interior homogeneity" and the "exterior differentia" of the masses, combining with the analyzing and the checting in statistics, there are every reason to distinct them into two different water masses. In this paper, some further modifying of the methods mentioned above are made and fitsout another membership function of the Sub-Intermediate Water Mass - enveloping curve method, construct new membership function for fitting the mixing of three water masses with vertical stratification.This paper uses the SCS climatic year-averaged data and the winter/summer data of 1998 monsoon experiment, which were provided by the South China Sea Institute of Oceanology. And provide the distribution of the sub-surface water mass with high-salinity, intermediate water mass with low-salinity and the sub-intermediate mixing water mass in the standard layer of the whole area of the SCS and in some representative profiles through the methods mentioned above. This paper mainly uses the coordinate turning method and the enveloping curve method to calculate and analyze three wate rmasses distributed vertically. The results are as follows:(1) The path of the Kurushio sub-surface water spreading towards SCS is: In summer, after passing through Bashi Channel it goes westward along the north shelf of the SCS, then spreads southward along west boundary, finally it spreads south and south-east and all over the SCS; in winter, after passing through Bashi Channel it spreads directly towards south-west crossing the SCS, after reaching the middle of Zhongnan Peninsula it spreads south-east. Totally speaking, sub-surface water is strongest in about 125m.(2) The Sub-Intermediate mixing water is produced by the processes of mixing and modifying of sub-surface water and Intermediate water. After these two water masses acrossed the Bashi Channel and then spreading to the SCS, the sub-surface water and the intermediate water mix and transform, and step by step enhance the thickness and intensity of the sub-intermediate water, so its distribution is just opposite to the sub-surface water and the intermediate water, and strongest is mainly in 200m-250m.(3) The intermediate water appears at the depth of 300m. And its spreading path is:...
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