I performed the research about the drinking water treatment by precoat filtration and activated carbon adsorption process in the D water treatment plant at Gwangju. D water treatment plant inlet water is supplied from Juam lake in Jeollanamdo. The results are as follows; 1. Element disk used in this experiment are R(pore size $10{mu}m$), B(pore size $20{mu}m$). And diatomaceous earth are A(cake pore size $3.5{mu}m$), B(cake pore size $7{mu}m$) and C(cake pore size $17{mu}m$) 2. Filtrate of precoat filter during 30 min are B-C 10.2 > BB 5.7 > R-A 5.4 ($m^3/m^2$). 3. The water quality through B-C+AC and R-A+AC are DOC 1.76 mg/1, 1.288 m/l respectively. 4. total THMs produced by chlorination are $84.2{mu}g/l$(B-C+AC), $66.11{mu}g/l$ (R-A+AC), $97{mu}g/l$ (rapid sand filtration water) respectively. 5. The R-A+AC and B-C+AC process can be substitute of CWTS.