In order to investigate the relation between the marine environmental characteristics and the change of the catch in set net, the marine environment properties were analyzed by temperature and salinity observed in the western coastal area of Cheju Island from 1995 to 1996 and the results are as follows 1) Main axis of Tsushima Current appeared in the western coastal area of Cheju Island was off 2$~$3 miles from November to May. Therefore the waters of high temperature over $14^{circ}C$ and high salinity from $34.40\%_{circ}$ to $34.60\%_{circ}$ were distributed homogeneously from surface to bottom in this time. But China Coastal Waters of low salinity appeared in the Cheju Strait from June to October, surface waters became of high temperature and low salinity, and middle and bottom waters became of the temperature from 11 to $14^{circ}C$ and the salinity over $33.50\%_{circ}$ and then vertically sharp thermocline and halocline are formed in the western coastal area of Cheju Island. In summer, the water temperature and salinity of the surface waters in wstern coastal area of Cheju Island were lower and higher respectively than that in middle area of the Cheju Strait and the temperature and salinity of the bottom waters in this area were higher and lower, respectively than that in middle area of the Cheju Strait. Such a distribution shows a tidal front in this coastal area. On the whole year, surface temperature and salinity were from 14 to $23^{circ}C$ and from 30.60 to $34.60\%_{circ}$, respectively, and annual fluctuation range of temperature and salinity was within $9^{circ}C$ and $4.00\%_{circ}$, respectively, Thus, annual fluctuation range in this area is much narrower than that in the Cheju Strait. In bottom water, temperature ranges from 14 to $20^{circ}C$ through the year. Thus, the fluctuation range of temperature is narrow. The low temperature of from $11^{circ}C$ to $13^{circ}C$ appeared in the west enterance of Cheju Strait was not shown in this coastal area. 2) The salinity of bottom water was from $33.60\%_{circ}$ to $34.40\%_{circ}$ in 1995, while low salinity wale. below $32.00\%_{circ}$ appeared all depth from June in 1996. Thus, the variation of hydrographic conditions in this area is narrow in winter, and wide in summer due to the influence of China Coastal Waters. 3) In summer, surface cold water, local eddy and fronts of temperature and salinity were showed within 2 mile from the west coast of the Cheju Island due to vertical mixing by tidal current. Especially, temperature and salinity of bottom water are changed with the change of depth around Biyang-Do. Thus, the front of temperature and salinity appeared clearly between shallow area with the depth of under 10 m and deep area with of the depth of more than 50m. Surface water in outside area where high temperature and low salinity water appear intrudes between Worlreong-Ri and Geumreung-Ri. Thus, the front of temperature and salinity was made along the line that connects from this coast to Biyang-Do, The temperature of the bottom water is $2^{circ}C$ to $4^{circ}C$ lower than that of the surface water and its salinity is $0.02\%_{circ}$ to $0.08\%_{circ}$ higher than that of the surface water even in shallow area.