To identify the cumulative influence of water diversion projects on the hydrological regime in the middle and lower reaches of the Hanjiang River, by setting up three different prediction scenarios and using a one-dimensional hydrodynamic model, the evolution characteristics and trends of flow and velocity under the joint operation of water diversion projects and seven cascade hubs in the middle and lower reaches of the Hanjiang River were analyzed. The results show that after the water diversion projects such as the first phase of the Middle Route of the South-to-North Water Diversion Project, the Hanjiang River-to-Weihe River Diversion Project, the Water Resources Allocation in Northern Hubei Province, and the Water Diversion Project from Yangtze River to Hanjiang River, the runoff process in the middle and lower reaches of the Hanjiang River has been significantly reduced and leveled. In typical normal years, the annual average flow at Huangjiagang, Huangzhuang and Xiantao sections decrease by 38%, 28% and 18% respectively, and the annual average velocity decrease by 9%, 9% and 3% respectively. In typical dry years, the annual average flow at Huangjiagang, Huangzhuang and Xiantao sections decrease by 27%, 22% and 1% respectively, and the annual average velocity decrease by 13%, 8% and 1% respectively. After superimposing the influence of the Water Diversion Project from the Three Gorges Reservoir to the Hanjiang River, the cumulative adverse effects of the water diversion project are weak. In typical normal years, the reduction rate of average annual flow and velocity at Huangjiagang, Huangzhuang and Xiantao sections remain basically unchanged. In typical dry years, the average annual flow at Huangjiagang and Huangzhuang sections decrease by 16% and 12% respectively, and the average annual velocity decrease by 4% and 3% respectively. The average annual flow and velocity at Xiantao section change from a decreasing state to an increasing state of 4% and 2%, respectively. The maximum increases in flow during the dry seasons in typical dry years at the Huangjiagang, Huangzhuang, and Xiantao sections increase from 139%, 91%, 160% to 201%, 146%, and 173%, respectively, improving the hydrodynamic conditions, and making probability of flow larger than the minimum discharge flow at Huangjiagang section increasing from 75% in Scenario One to 94% in Scenario Two and 98% in Scenario Three. The middle and lower reaches of the Hanjiang River still face ecological and environmental risks such as the difficulty in ensuring the minimum discharge flow in some periods and the ecological flow during the sensitive period due to the reduction in water volume, and the possible occurrence of algal blooms. It is suggested to study and propose an ecological flow dispatching plan for the middle and lower reaches of the Hanjiang River by comprehensively considering the cumulative influence of water diversion projects on hydrological conditions.