The abnormal low water temperature phenomenon of the Yellow Sea Bottom Cold Water in summer, 1981 is studied on the basis of the oceanographical data collected by the National Fisheries University of Pusan in July, 1981 and Fisheries Research and Development Agency of Korea from 1960 to 1981 and meteorological data within the same 22 years. In winter, 1980 the northwesterly monsoon was vary predominant and the air temperature was lower than that of mean year by 1∼8$^{circ}C$ and also the surface temperature was lower 1∼3$^{circ}C$. And then the temperature of the Yellow Sea Bottom Cold Water in summer, 1981 became lower 2∼3$^{circ}C$ than that of mean year and the influence of this cold water was extended to about 50 miles off the coast of Cheju Island. Comparing with mean year, the water temperature at 30m depth in February, 1981 was lower by 1∼2$^{circ}C$ in entire regions except near sea of Sohuksando and at 50m depth in August, 1981, it was lower by about 3.5$^{circ}C$. Particularly, the offshore of Hongdo shower value of 5$^{circ}C$ than that of mean year. It was found that the abnormal low water temperature phenomenon of Yellow Sea Bottom Cold Water in summer, 1981 resulted from the sea surface cooling by the predominant northwestly monsoon and abnormally low air temperature in winter, 1980.