The peak-load regulation of a coal-fired power plant is critical to promote renewable energy power generation in grid systems. A low-temperature multi-effect distillation (LT-MED) was proposed to improve the dispatchability of a 600 MW coal-fired power generating unit; here, an unsteady thermal system model was established using the Ebsilon software to study peak shaving capacities. The results show that the increased extraction amount and pressure will reduce the power generation and increase the coal consumption. The peak shaving capacity curve was obtained based on the extraction amount. It is indicated that the peak shaving capacity can reach a maximum of 477 MW when the amount of steam extraction is less than 238 ton/h. When the amount of extraction is sufficiently large, the exhaust steam from the low-pressure turbine attains the minimum allowable value, the peak shaving capacity of the unit then sharply decreases. The dynamic response of an LT-MED system to the step variation of the output load of the power generating unit was also revealed. Moreover, the power generation and coal consumption are slightly influenced by the steam consumption in a single LT-MED system. The maximum extraction of the unit can afford a maximum of 19 LT-MED systems. The results of this study will provide a useful reference for the peak shaving of coal-fired power generating units.