The coordinated operation of coal-fired power plant (CFPP) with large-scale energy storage systems can effectively regulate the flexibility of power system and smooth the renewable power output. A gas-liquid interconversion carbon dioxide energy storage system coupled with a CFPP was proposed, which recovers compression heat using condensate and feedwater of CFPP and preheats turbine inlet CO2 through drain water, realizing thermal decoupling of charge and discharge processes without heat storage devices. Based on the mathematical models of the coupling system, the system coupling schemes were designed and optimized, and a comparative performance analysis with stand-alone system was conducted. The results show that, the compression heat cascade recovery boosts the exergy efficiency of last-stage intercooler from 73.3% to 89.6%, and the exergy efficiency of the first-stage preheater improves from 53.1% to 89.7% by replacing extraction preheating with drain water cascade preheating. In the optimal coupling scheme, the system energy storage efficiency improves from 63.6% to 76.8% compared to the stand-alone system, and the levelized cost of electricity reduces from 0.130 dollar/(kW·h) to 0.093 dollar/(kW·h), with a slight reduction in round-trip efficiency to 63.2%. The turbomachinery and heat exchangers, representing the main contributors to the total system exergy destruction and investment cost, are key components in improving thermodynamic and economic performance. Increasing the discharge power to 90 MW reduces the levelized cost of electricity to 0.089 dollar/(kW·h) and expands the peak regulating range to 86.4%~107.6%.