Abstract: Fast and accurate identification of weak buses is of great importance for the secure and stable operation of power system. For this purpose, a power system decoupling model was developed, and a visual method for predicting weak buses in prospective operating conditions was proposed. Firstly, two-bus virtual channels were constructed for power system decoupling. Accordingly, each bus was endowed with a unique voltage index, and a voltage stability boundary was introduced. Then, the holomorphic embedding method with a scalable embedded factor was proposed to derive analytical expression of voltage index trajectory. Thus, the buses whose voltage index trajectories cross the voltage stability boundary were identified as the weak buses in the prospective operating conditions. Test results on the IEEE 14-bus, 39-bus and 118-bus power systems validate the effectiveness and accuracy of the proposed method.