In this paper, the removal efficiency of THMs (Trihalomethanes) and DOC (Disolved organic carbon) was compared under different GAC (Granual activated carbon) filling methods. One method is "full filling method" in which column is fully filled with GAC at once and the other is "periodic cumulative method" in which column is partially filled with GAC (10, 20, 33 and 50% of total column volume) and added each ratio during 300 days. The effluent concentration of both THMs and DOC under full filling method was low during the initial period, however, steadily increased with operating time. In the contrast, with periodic cumulative method, it maintained (relatively) evenly during the operating period. Periodic cumulative method was more efficient for removing THMs than full filling method. However, when the ratio of chlorodibromomethane or bromoform among THMs was significantly higher than chloroform and bromodichloromethane, full filling method was more efficient than periodic cumulative method. Full filling method had benefit to total DOC removal and control of average DOC concentration in effluent. Overall, periodic cumulative method is more efficient to equalize the removal efficiency of THMs and DOC, so the more frequent refilling of column with small amount of GAC is more advantageous.