Abstract: The river network connectivity is an important basis for the flood control, water supply and ecological security. An improved evaluation method based on hydraulic resistance and the graph theory is put forward. This method takes into account not only the capacity of different channel types, but also the operation conditions of the sluices including closing and opening conditions, which was never considered in previous methods. The method has been applied to the evaluation of the river network connectivity in the plain area of the Taihu basin, which is a typical complex system of the "nature and artificial". By using the water quantity and quality model for Taihu basin, the structure sketch map of the river network can be established, the water levels of all the rivers and the opening degree of the sluices in the basin can be calculated, and weighted adjacent edge matrix can be set up finally. Using MATLAB, the connectivity degree of the river network in a typical year (1990) can be estimated relatively quickly. The overall evaluation results show that the overall connectivity degree of the total water system in the plain area of the Taihu basin is high, but there are some differences among each water resources district: the connectivity degree of the Yangchengdianmao and the Taihu district is the maximum. The evaluation result conforms to the actual situation and is consistent with the conclusion of the previous research conclusions.The method realizes the quantitative evaluation of the connectivity in the plain river network area, and can be used for water system connectivity assessment so as to improve the design of the water network system.