Effectiveness of soil and water conservation has been focused on sediment control; whereas the flood and runoff retention has not received equal attention so that quantitative assessment has seldom been able to reach and provide recommendation for slopeland management. Therefore, this study applies FLO-2D to assess the effectiveness of runoff retention at Tainan Agricultural Research Extension Station, Xinhua District, and Wangliao, Neiwan District, Kaohsiung City. Results of numerical simulation include the changes of runoff hydrographs, lags of peak flow arrival time, and reductions of peak runoff rates prior and after degrading operations of farm ponds. The simulation results provide recommendations for future slopeland management particularly for the purposes of runoff reduction and flood mitigation.