The available residual chlorine was produced by seawater chlorination. The available residual chlorine could be removed by UV light irradiation. But the degradation rate of available residual chlorine can not be affected by water flow rate (p>0.05). The total ammonia-N (about 1 mg/l) could be removed 50 % by 6 mg/l free available chlorine of sodium hypochlorite under no UV light irradiation. But the total ammonia-N (about 1 mg/l) could be removed 60 % by 6 mg/l free available chlorine of sodium hypochlorite under UV light irradiation. Therefore, the UV light irradiation will good for the ammonia removal in seawater. Different concentration of glucose or humic acid in seawater did not affect the removal of ammonia by 6.0 mg/l free available chlorine of sodium hypochlorite (p>0.05). But 25 mg/l glucose or 1.0 mg/l humic acid of seawater could affect the disinfection of 6.0 mg/l free available chlorine of sodium hypochlorite (p<0.05).