Abstract: The utilization of surface water resources is difficult in coastal areas due to short flow path and sharp gradient of river channel. Incorporating unconventional water resources such as reclaimed water and desalinated seawater into unified urban water systems in coastal cities is an effective way to alleviate water shortage. A key point to realize the unified allocation of conventional and unconventional water resources is to scientifically determine the construction scales of unconventional water sources considering uncertainties of conventional water resources. In this paper, an optimal model for determining the construction scales of desalinated seawater and reclaimed water considering inflow uncertainties is established through a case study in Weihai City. The non-dominated sorting genetic algorithm-Ⅱ is adopted to solve the model. Three indexes (reliability, resilience and vulnerability) are used to measure the performance of the whole water supply system and further compare results with the current basic scheme. The results indicate that at the planning level of 2030, the suitable construction scales of reclaimed water and desalinated seawater in Weihai urban area are 230 thousand m³/d and 150 thousand m³/d respectively. Based on these scales, the guarantee rate of urban water supply in Weihai urban area increases from 63.8% to 95.2%, and the average annual water supply cost is 660 million yuan. The results can provide decision-making reference for regional water supply planning.