Abstract：To study the optimal conditions for the biodegradation of cholrobenzene(CB)-contaminated ground water by immobilized microorganism, the CB-degrading bacteria are screened out from the CB-contaminated soil. Polyving alcohol (PVA) and sodium alginate are used to encapsulate microorganisms to make immobilized bacteria beads. The optimal conditions of the immobilized beads were identified by the orthogonal experiment, with the effect factors including mechanical strength, penetrability and the removal efficiency of the CB. The factors influencing the immobilized microorganism degrading ability were studied. The results show that the removal efficiency of the immobilized beads is better than the free microorganism. When the immobilized beads are in the optomal condition with the diameter of the bead being 1mm, the concentration of bacterial suspension 8%, the initial concentration of CB 80mg/L, pH value about 7.0, the concentration of the NaCl less than 1.5%, the temperature 10℃, and the shaking table revolution 120r/min, the biodegrading performance is quite excellent.