In the southern tidal area, it is indispensable to fully unearth and develop the potentialities of a reservoir for the flood detention and storage, which can make the reservoir fully display the functions of the flood detention and thefresh water storage, effectively relieving severe waterlogging disasters and the problem of insufficient water supply due to the influence of saline. Take the Tianxin reservoir located in the Zhong-Zhu union catchment of Guandong province as an example, these were described in detail including the train of thought about exploiting reservoirs potentialities and methods of making a regulation for the reservoir operation and parsing process. To make a regulation for the reservoir operation is a difficult point, because it must take some factors into account, such as changing rules of outer water level and regional drainage situation. An reservoir revamping is studied at the original catchment area first. By setting 4-meter-high gate on the spillway and using the rational operation regulation, it is possible to reserve a maximum flood of 6 h for the peak shifting and increase the beneficial reservoir capacity by 1. 21 million m³ without increasing the dam height. Then, combining the terrain around reservoir region, the flood of the west shoulder is led to the Tianxin Reservoir. The revamping research with increasing catchment area indicates that by setting 6-meter-high gate on the spillway, increasing dam height by 2 m and using the rational operation regulation, it is possible to reserve a maximum flood of 6 h for the peak shifting as well and increase the beneficial reservoir capacity by 1. 93 million m³.