The sodium alginate fossilization Sphingomonas strains have double features: the biological absorption and biological degradation. And through using them to remove COD in the seawater we can see the pH value has highly significant impact on the removal rate, in addition, when the temperature is 37°C, pH value is 7.0, the pellet concentration is 1.0 g/L, the rotating speed is 120 r / min and oscillate for 90 min, the removal effect is the best. Pure strains, embedding micro-organisms have better removal efficiency of COD, indicating that microbes play a major role on the removal of COD, and microbial removal efficiency is the best after cultivated for 24 h, for microorganism is in the strongest logarithm phase at that time. However, the adsorption of COD mainly comes from functional groups on the surface of sodium alginate adsorption. The removal rate of COD in seawater treated by immobilized thallus can reach 86%, and can reach Class Ⅱseawater quality standards after purified. The study has the features of maintaining the multi-enzyme system of microbial cells, having less effect on microbial activity and also having obvious treatment effect; furthermore, its operation is simple, it requires less equipment and with lower prices.