Mine water cannot be discharged until it has been treated, which increases the cost of mining and causes environmental damage. This paper attempted to use sulfate mine water as a flame retardant material for the treatment of coal spontaneous combustion (CSC) in underground mines. The temperature-programed experimental device and gas chromatograph were used to simulate the low-temperature oxidation process of coal. Infrared spectroscopy was used to study the influence and inhibition mechanism of mine water and chloride inhibitor on active functional groups. It was found that although the sulfate mine water inhibited the formation of −OH, it accelerated the cleavage of the aromatic ring. The thermogravimetric experiment was used to analyze the ignition temperature and activation energy of different coal samples. It was found that mine water had an obvious effect on inhibiting CSC in the combustion stage, which could increase the oxidation temperature of coal.