Under the background of rapid urbanization, it is an important mean to enhance the storage capacity of precipitation and reduce the damage losses from floods by guaranteeing the suitable water surface ratio based on the functions of flooding transfer and drainage management. In this study, by considering the rainstorm intensity and the underlying surface conditions, the method of the suitable water surface ratio determination for flooding transfer and drainage management is proposed. Taking Bengbu City in Anhui Province, a national key flood control city as an example, surface runoff yield from various underlying surfaces was calculated under different standards of flooding transfer and drainage management for a certain rainstorm intensity. Then the drainage capacity was planned to increase through reducing paddy field area and increasing water area with a consideration of required drainage capacity, and the suitable water surface ratios were calculated. In Bengbu city, the suitable water surface ratio is 12.5%~19.5% under the standard of one day rainstorm amount in 50 year returning period and three days rainstorm amount in 100 year returning period. The research route and calculation methods can provide references for the research of suitable water surface ratios in other regions and have great significance to urban planning and ecological environment management oriented towards regional water security.