<p>Identifying weak lines and prioritizing their reinforcements are crucial for enhancing power system reliability. However, when analyzing operational risks from various perspectives, it is necessary to define different indicators that accurately depict the characteristics of risk. The identification results based on different indicators are often inconsistent. The determination of the relative impact on the consequences of a fault line during multiple faults is also challenging. In light of these challenges, this paper presents an identification methodology for the weak lines in the power grid based on Shapley-TOPSIS (S–T). This methodology assesses the vulnerability of weak lines under simultaneous fault conditions. It initially employs Shapley values to determine the allocation modality of failure value under each indicator. Subsequently, based on multiple vulnerable indicators, TOPSIS is exploited to undertake a comprehensive ranking of each component, thereby quantifying the vulnerability of each element in the system. The illustrative analysis demonstrates that the S–T method effectively identifies critical weak lines within limited reinforcement costs, thereby minimizing load shedding and reducing potential shutdowns affecting essential loads while also minimizing expected fault occurrences.</p>