The probabilitic Budyko equation is used to quantitatively evaluate the spatial distribution of water availability in China and its corresponding uncertainty, and identify the regions with high vulnerability of water availability in China. The results show that precipitation is the dominant factor for the vulnerability of water availability, and the uncertainty is smaller in arid regions. The water availability in Northeast China, Northwest China, North China and East China are most susceptible to precipitation variability, and this phenomenon is still evident under different precipitation decreases(5%, 10% and 15%, respectively), the regions are highly vulnerable to precipitation change.