To address the risks to the safe and stable operation of the power grid and the challenges in power balance caused by the high penetration of renewable energy, while promoting the effective consumption of renewable energy and alleviating the peak-valley load disparity, this paper proposed a three-part tariff mechanism based on the functional positioning of coal-fired power units. Firstly, we analyzed the three functions provided by the coal-fired power units under the new power systems, including basic power security, consumption of renewable energy and auxiliary service. Secondly, the cost composition of coal power units was analyzed. Thirdly, a three-part tariff mechanism was constructed based on the values provided by the coal-fired power units, including power value, regulation value and capacity value, and cost pass-through was carried out via diversified routes. Finally, a sensitivity analysis of the cost pass-through of coal-fired power units was conducted under different capacity subsidy ratios and auxiliary service prices. The results show that based on a benchmark coal price of 675 yuan/ton, under the scenario of a 30% coal price increase, the total per-kilowatt-hour costs for coal power would be 42.09 cents/(kW·h), 39.73 cents/(kW·h), and 38.16 cents/(kW·h) respectively when implementing no capacity subsidy, 30% subsidy, and 50% subsidy. Compared with the original coal price scenario, these represent increases of 20.9%, 22.4%, and 23.6% respectively. The proposed three-part tariff mechanism can stimulate the initiative of power units in peak shaving, ensure the power units to provide sufficient standby capacity, and incentivize the power units to participate in the system FM service, thus fully stimulating the vitality of the coal power in the power market.