To make up for the deficiency that graph theory can not consider the dynamic transmission capacity, the HEC_HMS hydrological model is set up to simulate the flow, and construct the connectivity factor that characterizes the exchange capacity of river network and the hydrologic connectivity evaluation model based on improved graph theory and hydrological simulation on the basis of using graph theory about connectivity degree to evaluate the connectivity condition of river network. The case evaluation results of the river network hydrologic connectivity in the Qinhuai River Basin indicate that the connectivity degree of Qinhuai River Basin decreased from 0.004 4 in 2000 to 0.002 9 in 2010, and the river network hydrologic connectivity level is not high in 2010, which is in line with the actual situation. The results of this evaluation model are reasonable and reliable.