Based on the in-situ data collected around Hong Kong sea area and its vicinity from March to May in 2001, spectral characteristics of water color components are analyzed. For establishing retrieval algorithm, the empirical mode between chlorophyll-a concentrations (Chl.a) and phytoplankton pigment absorption coefficients a_ph(675) is developed with a significant correlation. Relationship between total suspended matter concentrations (TSM) and de-pigment absorption coefficients a_d(440) is calculated. Underwater data which contain apparent optical property spectra are used to extrapolate water remote sensing reflectance (r_rs). A semi-analytical algorithm is developed to retrieve Chl.a which is compared with in-situ measurements lastly. The mean relative error is 45%, the correlation coefficient is 0.78, and the root mean standard error is 0.933. Results show that the algorithm is suitable for the study area with low concentrations of TSM and chlorophyll-a.