Abstract: With the frequent occurrence of geopolitical conflicts, the vulnerability of the global natural gas trade has escalated significantly. A scientific emergency regulation and supply guarantee mechanism should be established to safeguard national energy security. A two-stage demand-side regulation model under extreme scenarios is proposed. The precise allocation of natural gas quotas across different provinces and sectors is achieved by this model. First, a comprehensive evaluation index system for sectoral importance is constructed. This system is established from three dimensions: macroeconomic impact, industrial chain network vulnerability, and social livelihood baseline. The Inoperability Input-Output Model (IIM), complex network theory, and Bayesian probability updating are innovatively integrated. Second, a two-stage regulation model based on multi-objective optimization is formulated. The minimization of the three-dimensional comprehensive losses is set as the joint objective. In the first stage, the Pareto optimization of national sectoral regulation schemes is realized using an improved NSGA-II algorithm. In the second stage, regulation directives are accurately decomposed into provincial quotas. An iterative allocation rule based on "baseline priority and margin equal sharing" is applied. Strict constraints on the baseline demands of all provinces and sectors are thereby ensured. Three scenarios of natural gas import disruptions with varying severity levels are simulated. These simulations are based on the 2023 input-output and energy data. The results indicate the following: (1) under a mild shortage (6%), the supply strategy is driven by marginal benefit maximization. Supply-demand balance is achieved by slightly adjusting high-energy-consuming sectors. (2) Under a moderate shortage (26%), distinct regional supply-guarantee features are exhibited. Greater regulation responsibilities are forced upon provinces like Shandong and Yunnan. This is required to preserve core technological industries in other regions. (3) Under an extreme shortage (42%), the mechanism is evolved into a baseline defense strategy. Resource allocation is highly concentrated on maintaining core social functions, such as residential living and strategic transportation. Consequently, regional disparities are intensified. It is recommended that the natural gas emergency regulation mechanism be upgraded towards refinement, quantification, and dynamization. Cross-provincial emergency regulation mechanisms should be explored. Differentiated gas utilization guidance should be implemented to enhance sectoral demand elasticity. Quantitative decision-making support is provided for the refined governance of the national natural gas emergency supply system. Precise guarantees under natural gas crisis scenarios are thereby facilitated by these findings.