China’s social security system is confronting a structurally compounded challenge arising from accelerated population aging and a sustained increase in life expectancy. Under the pay-as-you-go (PAYG) financing mechanism, the Urban Employee Basic Pension Insurance (UEBPI) fund faces significant financial imbalance risks. In 2024, the State Council adopted the Measures on Gradual Delay of Statutory Retirement Age (hereinafter referred to as the “Measures”), which aims to alleviate fund pressure by adjusting labor supply and the benefit claiming cycle. However, the net impact of the delayed retirement policy on pension sustainability, as well as its interaction with longevity risk, requires actuarial quantification based on the latest policy parameters. This study employs a cohort-component model and incorporates the Niu-Melenberg (NM) dynamic mortality model to project future mortality trends, thereby integrating longevity risk into the actuarial evaluation framework. Building on this, and in accordance with the gradual adjustment schedule stipulated in the “Measures”, this study constructs an actuarial model that differentiates among “legacy” , “transitional” and “new” cohorts, as well as by occupational categories. Key indicators include the fund’s annual deficit, cumulative deficit, and the ratio of its fiscal liability to GDP. Through cross-scenario analysis, this study identifies the optimal synergy range between the delayed retirement policy and core institutional parameters, including the contribution collection rate, contribution rate, and coverage rate. Empirical results indicate that longevity risk intensifies financial pressure on the pension system. Under the dynamic mortality scenario, the cumulative deficit-to-GDP ratio is 3.16 percentage points higher than under a static mortality assumption. The gradual delayed retirement policy effectively improves the contributor-to-beneficiary ratio and postpones the onset of cumulative deficit to 2032, substantially reducing fiscal obligations at the end of the projection horizon. Nevertheless, the policy exhibits diminishing marginal returns, and delayed retirement alone cannot fundamentally reverse the long-term deficit trajectory. Further analysis reveals that a combined strategy of enhancing the contribution collection rate and expanding coverage yields the strongest policy synergy, delaying the emergence of the cumulative deficit to 2042. This combination represents the critical pathway toward achieving long-term actuarial balance. This paper contributes to the literature in two key respects. First, it constructs a dynamic actuarial model that is fully consistent with the latest policy parameters and gradual pace of the “Measures”, revealing the coupling mechanism between the delayed retirement policy and longevity risk. Second, it embeds a dynamic mortality model within the policy evaluation framework, enabling the quantification of longevity risk and offering a novel approach to establishing an actuarial balance mechanism for China’s pension system. The findings provide actionable insights for policymakers to design targeted, complementary institutional reforms alongside the rollout of the delayed retirement policy, thereby enabling the provision of differentiated and refined policy support to ensure the long-term sustainability of China’s social security system.