Sensitivity analysis for water supply risk in the area  influenced by interbasin water transfer is presented in the paper. Taking the influenced area of the middle route of South-to-North Water Transfer Project, which is also known as the main stream area of middle and lower Hanjiang River, the authors investigate the risk source of water supply in the source region of the Project and its three major influencing factors as water inflow, water demand, and water transfer. Stochastic simulation, long-sequence reservoir routing, orthogonal test, and  analysis of  range are employed to calculate the sensitivities of water supply risk to the three influencing factors. The result demonstrates that the risk index of water shortage in the area is most sensitive to the water demand of the middle and lower reaches, followed by the water inflow into Danjiangkou reservoir and the water storage transferred through the middle route of the Project.