The quantitative analysis of hydrological connectivity between lakes and river systems serves as a fundamental guide for the conservation and management, and it represents a current focal point in the research on the ecological restoration of rivers and lakes. This paper introduces a quantitative calculation model for assessing the hydrological connectivity between lakes and rivers. The model requires minimal empirical or hydraulic simulation data for validation, enabling the quantification of hydrological connectivity in single or multiple connecting channels between rivers and lakes. Water level and its change rate are crucial parameters. The change rate of water level is linearly related to the intensity of water exchange, while the water level is positively correlated with the rate of increase. The proposed empirical formula for water exchange flow can effectively estimate the exchange flow between lakes and the Yangtze River. Under equivalent water levels and rates of water level changes, the efficiency of outflow from lakes to the Yangtze River exceeds that of inflow from the Yangtze River to lakes. The peak value of hydrological connectivity generally occurs at points of variation within the overall rising or falling range. Hydrological connectivity can be effectively increased by adjusting the process of water level rise or decline, which can guide ecological scheduling aimed at improving the aquatic ecosystem in lakes.