Abstract: As a strategic pillar of low-carbon energy systems, nuclear power’s sustainable development fundamentally depends on operational safety. Catastrophic accidents at Three Mile Island, Chernobyl, and Fukushima have demonstrated the severe threats posed by reactor core damage events. These events involve complex multi-physics phenomena, including core melt progression, molten corium relocation, containment failure mechanisms, and radionuclide release. Given the prohibitive challenges, and often impossibility, of experimentally replicating such extreme conditions, highly reliable severe accident (SA) analysis tools become essential. These tools are vital for deciphering accident sequences, optimizing mitigation strategies, and ultimately ensuring reactor safety. Currently, a critical vulnerability exists in China’s engineering capabilities for SA analysis, which remains significantly dependent on foreign commercial software. The imposition of post-trade war technology embargoes on these crucial codes has severely constrained China’s domestic nuclear autonomy and hindered the international market expansion envisioned under its “go global” strategy. To address this technological gap and bolster national safety research while supporting indigenous pressurized water reactor (PWR) development, Xi’an Jiaotong University has developed CAP (containment analysis program under severe accidents). CAP serves as an integrated analysis code specifically designed to simulate the response of PWR containment structures during both thermal-hydraulic transients and severe accident scenarios. Its computational architecture integrates and couples a robust thermal-hydraulic module with specialized SA physical models critical for containment behavior prediction. These core SA physical models encompass phenomena such as radionuclide transport, molten corium-concrete interaction (MCCI), direct containment heating (DCH), and other key physical processes relevant to PWR containment experiencing severe accidents. To verify CAP’s accuracy and validity under severe accident conditions, representative international experimental benchmarks (NUPEC M-8-1, AHMED, CCI-4, and IET-1) were simulated. The calculated results from CAP were systematically compared against the available experimental data. These verification studies demonstrate that the CAP program’s calculations align well with the experimental results. This validation confirms that CAP can effectively simulate essential severe accident phenomena within the containment environment, encompassing thermal-hydraulic transients, radionuclide migration behavior, molten core-concrete interactions, and direct containment heating events. CAP thus presents a domestically developed solution that directly addresses the pressing technological vulnerability in severe accident analysis. Its deployment contributes significantly to nuclear safety research and strengthens China’s independent nuclear power capabilities.