Abstract: The Lancang-Mekong River (LMR) basin has historically been affected by severe floods and is likely to suffer further flood events with higher peaks and longer duration in the future due to climate change, which calls for collective action to respond. This study examined the potential flood control effect of coordinated operation of the LMR transboundary multi-reservoir system by establishing a distributed hydrological model coupled with a reservoir operating model, simulating the runoff of 13 tributaries and 5 mainstream sections. Results show that:① Flood magnitude at the five sections along the Mekong River is significantly reduced by mitigating flood recurrence from 200 years to 20-50 years.② In terms of flood control, the left-bank tributaries contribute more than the right bank. Tributaries with relatively higher flood control capacity are:Lancang, Nam Ou, Nam Ngum and Nam Theun, Nam Mun, Se Kong and Se San. ③ Different tributaries play a major role in flood control across regions. Luang Prabang's main flood control tributaries are Lancang and Nam Ou. At Nakhon Phanom, Lancang's flood control contribution is same as Nam Ngum and Nam Theun's sum. In the downstream of Pakse, the flood control contribution of Nam Mun and Se Kong are higher than Lancang. This research provides a reference for transboundary flood control cooperation between riparian countries, which face an important opportunity underpinned by the Lancang-Mekong Cooperation Mechanism (LMC).