An experiment was conducted to reduce sulfur oxides by burning low-calorie, low-sulfur sub-bituminous coal treated with an alkali metal-based coal pretreatment desulfurization agent. As a result of pre-combustion treatment with 0.3% desulfurization agent, it was possible to reduce sulfur dioxide by 96.83ppm from 97.10ppm to 0.27ppm on average compared to raw coal at 6% reference oxygen concentration, and the maximum reduction rate was found to be 99.70% on average. Additional research is needed on whether such a reduction rate is possible even in the case of high-sulfur coal treatment, but by using an alkali metal-based pre-combustion desulfurization agent, the emission of sulfur dioxide could be dramatically reduced for low-sulfur sub-bituminous coal. In the future, it will be possible to minimize the emission of sulfur dioxide to the atmosphere by operating in combination with FGD, which is a post-treatment facility.