During optical buoy experiments in the Pearl River (Zhujiang) mouth regions, time series of bio-optical data of Chaetoceros socialis red tide is obtained. By using the data, variation of ocean optical properties (absorption and backscattering properties) in the occurrence and declination of red tide is analyzed. Results show that the absorption of various components such as phytoplankton pigments, detritus and colored dissolved organic matter changes dramatically, the absorption of various components increases and reaches maximum values in red tide outbreak period, then the absorption of various components decreases and reaches minimum values in red tide declination period. Compared with red tide development and declination period, contribution of phytoplankton pigment increases by 16%, and that of colored dissolved organic matter decreases by 18%, but that of detritus has little changes for red tide out break period; backscattering coefficient increases in red tide outbreak period, and range of diurnal variation is large, backscattering coefficient is small in red tide development and declination period, and the value is minimum in red tide declination period. Correlation coefficient between backscattering coefficient and chlorophyll-a concentration is larger than that between backscattering coefficient and suspended matter concentration. Although concentration of particulate organic matter in the total suspended particulate matter dominates, correlation coefficient between the backscattering coefficient and particulate inorganic matter concentration is larger.