With the retrospective vulnerability evaluation of watershed water resources sustainability, not only can the potential risks impacting watershed sustainability be identified, but also the watershed sustainability capacity and implementation effect of water resources policies can be evaluated, which would provide some guidance for the government to improve and optimize the existing policies. A n-dimensional space evaluation model for watershed water resources sustainable vulnerability was established using time series analysis method, based on Euclidean space theorem. Furthermore, the state space model was used to analyze the sensitivity of total vulnerability to the dimensions of resources, environment and socio-economy in time series. Finally, Xiangjiang Watershed was adopted as a case study to verify this model. Results show that the total vulnerability of water resources in this watershed showed an overall decreasing trend from 2007 to 2018, it was highly sensitive to the dimension of environment, moderately sensitive to the dimension of resources and slightly sensitive to the dimension of socio-economy. The conclusions of vulnerability evaluation show that the water resources management policies of Xiangjiang Watershed have achieved remarkable effects.