Based on a precise analysis of the long-term(1971-1984) hydrographic and wintertime air temperature data gathered in the middle and southern yellow Sea, and together with other supplimentary data from Gteratures, water characteristics of the Yellow Sea Bottom Cold Water(YSBCW) and its southward extension are reexamined ; the influence of the wintertime air temperature on the YSBCW temperature and on its spatial distribution also discussed. It was found that the hitherto defined water characteristics (T, S) of the YSBCW restrict especially the upper limit of salinity to too lower values compared to the real situation, so they are not adequate to describe the spatial distribution of the water and its southward extension phenomenon. From the present study, the southward extention of the YSBCW through the cold water through west off Chejudo from spring to summer is found highly possible ; it is strongest is April and it can be detected until August. In consequence of such a southward advection of the bottom cold water, the water temperature at 50m depth in the cold water through west off Chejudo shows its lowest values in April, with a mean temperature increase by 0.4℃ only from April to August(compared to 4℃ increase near the axis of the Yellow Sea embayment). The frequently observed cold water mass from the west to the southwest(near 32°N, 126°E)off the island during spring and summer is connected with and influenced profoundly by the bottom cold water from the southern Yellow Sea, showing almost same water. characteristics as those of the latter ; it preserves quite well its wintertime water characteristics until summer. Therefore it seems to be quite reasonable to include this cold water mass(found west to southwest off Chejudo) in the definition of the YSBCW. Here, we have suggested a new definition of the YSBCW : T$lt;12℃, 32.2$lt;S$lt;33.5‰ With this new definition, the spatial distribution of the YSBCW from the offshore of the Shandong peninsula to the southwestern area off Chejudo as well as its southward extension from spring to summer can be adequately described. The wintertime air temperature is one of the most important meteorological factors, controlling the summertime water temperature of the YSBCW and its spatial distribution. In other words, the bottom cold water formed during a severe cold winter exhibits in summer lower temperatures and also wider spatial distribution toward the coasts and to the south than that formed during a mild winter.