An assessment model for water resources carrying capacity (WRCC) in consideration of water conservation and water transfer was constructed with the maximum economic scale and maximum population sustained by corresponding WRCC as assessment indicators. The WRCC in Hanjiang River basin in different target years at varying water transfer scales was assessed as a case study. Under the scenarios of diverting 9.5 billion cubic meters of water for the Middle Route of South-to-North Water Diversion Project and in the mean time 1.0 billion cubic meters for the Hanjiang River-to-Weihe River Water Diversion Project, the water resources in Hanjiang River Basin could still support the potential for socio-economic development of the basin, and could even afford water transfer to other basins with a maximum amount reaching 1.97 billion cubic meters and 1.56 billion cubic meters in target year 2020 and 2030, respectively. Nevertheless, in the scenario of diverting 13 billion cubic meters of water for the Middle Route of South-to-North Water Diversion Project in 2030, the water resources in Hanjiang River Basin could no longer support the sustainable development of the basin, and external water compensation from outside the basin should be needed. In addition, a coordination degree model was constructed to evaluate the capacity of water resources sustaining socio-economic development on macroscopic level based on the theory of synergy with sequential parameters containing water consumption factor. From 2011 to 2017, the water resources carrying system in Xiangyang gradually developed from relatively uncoordinated to basically coordinated. The overall WRCC tended to develop soundly in consideration of water conservation. The research findings offer scientific basis as well as technical support for researching the trans-basin water diversion scale in the Hanjiang River basin in the long run and for determining the water compensation scale from the Yangtze River.