The complexity and heterogeneity of firm supply chain adjustment in response to major external shocks require identification through micro-empirical analysis grounded in theoretical frameworks. Using the 2011 Great East Japan Earthquake as a quasi-natural experiment, this study examines how Chinese firms responded to this major import shocks by transferring their supply chainsacross borders, based on merged data from the Chinese Industrial Enterprise Database and the Chinese Customs Import and Export Database from 2007 to 2014.The findings reveal that after the earthquake disrupted supply chains, domestic intermediate goods importers are more inclined to establish diversified supply chain relationships with firms in other countries or regions. Heterogeneity tests indicate this tendency are more pronounced among foreign-owned enterprises, processing trade firms, industry leaders, imported intermediates only from Japan before earthquake as well as firms that are highly reliant on inputs imports from Japan.Further analysis shows that firms’ transnational supply chain diversification does not imply global dispersion but rather exhibits characteristics of regionalization and proximity. The capacity for supply chain restructuring is influenced by both internal and external information environments: Firms with more developed internal trade networks, access to information channels through neighboring trading firms, and support from trade intermediaries are better able to leverage information spillovers to quickly identify alternative suppliers and achieve efficient restructuring.This study enriches the micro-level evidence on corporate supply chain adjustments under major shocks and provides empirical insights for firms seeking to mitigate external risks and enhance supply chain security and stability.