Against the backdrop of deepening population aging and mounting fiscal pressure on the enterprise employee pension insurance system, this study takes Jiangxi Province as the research sample. Employing a tri-level analytical framework of “demand–supply–satisfaction” security, and utilizing the cohort component method, pension actuarial models, and the ARIMA model, this study estimates both the fiscal risk mitigation effects from reducing the supply-side security level and the market demand space for the third pillar in Jiangxi from 2025 to 2050. The findings reveal that if the supply-side security level is adjusted downward to the demand-side security level, the percentage reduction in fiscal risk would decline from 13.81% in 2025 to 2.29% in 2050. This indicates that such a measure yields a notable mitigation effect only over the next 5–10 years, and is unlikely to serve as a fundamental institutional solution to deep population aging in the medium to long term. Over the same period, the continuous expansion in the number of insured retirees drives steady growth in the market demand space for the third pillar. When the relative share of the third pillar increases from 1/2 to 2/3, the market demand space is projected to reach approximately CNY 470 billion by 2050, demonstrating substantial development potential. This paper proposes two policy recommendations: on the one hand, grasp the window for supply‑side adjustment while simultaneously establishing a long‑term mechanism; on the other hand, accelerate the institutional improvement and product innovation of the third pillar to form an effective supplement to the first pillar.