With the rapid development of the renewable energy industry, thermal power units are increasingly required to provide peak shaving support within the power system. The integration of heat storage technology has emerged as a key strategy for enhancing the operational flexibility of coal-fired power units. However, existing solutions primarily rely on single-stage molten salt heat storage and release, which imposes limitations on overall heat storage capacity and efficiency. This study proposes a two-stage molten salt-water heat storage system and utilizes Ebsilon simulation software to model a 660 MW coal-fired unit. Three different heat storage and release schemes for the coupled molten salt-water system are comparatively analyzed in terms of peak shaving performance and thermal efficiency. The results indicate that Scheme 1 (heat storage via main steam extraction) achieves the highest peak shaving performance. When the heat storage power is 120 MW, its peak shaving capacity reaches 60 MW. Scheme 3 (heat storage via intermediate-pressure cylinder exhaust extraction) exhibits the highest thermal efficiency, reaching 40.5% at a heat storage power of 40 MW, with the efficiency increasing as the storage capacity grows. When the heat release power is 50 MW, Scheme 1 demonstrates the highest thermoelectric conversion ratio (29.9%), while Scheme 3 records the lowest overall thermal efficiency (38.4%) and the highest coal consumption per unit of electricity generation (301.2 g/(kW•h)).