Abstract: To address the water supply risks in the water receiving areas caused by different drought - wetness encounters of runoff between the water supplying and receiving areas of the middle route of the South-to-North Water Transfer Project, this paper constructed a Copula joint distribution function for the runoff of the water supplying and receiving areas based on measured data from representative hydrological stations from 1979 to 2023. This function was used to calculate the probability of drought and wetness encounter. The water availability of the receiving areas was calculated under different drought-wetness encounters. Based on the water availability, indicators such as water supply risk rate, resilience, and vulnerability were calculated to quantitatively analyze the water supply risks in the receiving areas. The results indicated that the Gumbel-Hougaard Copula function can effectively simulate the joint distribution of runoff in the water supplying and receiving areas. The drought - wetness encounter probability of synchronous in the runoff was 41.02%. When drought - wetness encounters in the water supplying and receiving areas were dry - dry, dry – extreme dry, extreme dry - dry and extreme dry - extreme dry, the occurrence probability was 13.53%, 2.36%, 2.36% and 0.61%, respectively. Among the water availability of Henan Province, Hebei Province, Tianjin and Beijing, the average proportion of transferable water quantity was 19.18%, 27.77%, 27.82% and 24.65% respectively, alleviating water scarcity pressures in these regions. The water supply risks in the receiving areas exhibited an upward trend with the decrease of runoff in the water supplying and receiving areas. When both areas experienced extremely dry years, the water supply risk in the receiving areas was at a medium risk level. The water supply risk in the receiving areas will further increase during consecutive dry years. The research results were of reference significance in ensuring the normal operation of the Middle Route Project of the South-to-North Water Transfer and the optimal allocation of water resources.