Plain lakes in Northern Jiangsu, such as the Luoma Lake, are afflicted by the spatiotemporal mismatch between water resources redundancy during flood seasons and water scarcity during non-flood seasons. To enhance integrated allocation efficiency of regional water resources, we developed a floodwater resources utilization scheme involving an appropriate raise of the flood limit water level (FLWL). A flood model was established for the Luoma Lake catchment, employing a flood volume scaling method to reconstruct inflow flood hydrographs during flood seasons. The elevation of the FLWL was designed under pre-release capacity constraints, and the scheme risks were quantified by flood routing calculations. The long-term reservoir regulation computation was employed to estimate the utilizable floodwater resources under different water level elevation scenarios (23.0 and 23.5 m), and the comprehensive benefits were analyzed from economic, social, and ecological perspectives. Results indicate that raising FLWL to 23.0 and 23.5 m increases annual utilizable floodwater resources to 138 million and 262 million m3, respectively. Correspondingly, the volume of surplus floodwater decreases from the baseline 3.648 billion to 3.407 billion and 3.174 billion m3, while annual water shortage reduces from 169 million to 136 million and 106 million m3, respectively. The comprehensive socio-economic benefit assessment reveals that the harvested floodwater resources can generate significant economic gains and enhance regional water supply capacity, with notable synergistic effects in maintaining lake ecological baseflow and alleviating regional water stress. The proposed technical method offers certain reference value for the analysis of floodwater resources utilization in plain regions.