Fuel switching technology is being applied to biomass as a way to reduce greenhouse gas emissions from coal-fired power plants. During the process of co-combustion with coal, biomass is subject to constraints of mixing ratio due to problems of milling, calorific value, and ash such as that of K2O and Na2O. In this study, the wet torrefaction(WT) process was operated at 160, 180, and 200℃, and the increase of the calorific value compared to the mass reduction of the miscanthus was analyzed. In the case of the WT process, unlike the simple torrefaction process, the ash contained in the biomass is extracted by water. XRF analysis of ash behavior showed that the K2O and P2O5 components in the ash relatively decreased as the pre-treatment temperature increased. In particular, compared with coal, biomass has K2O as a major component and this is a major factor causing combustion trouble such as clinker, fouling, and slagging. In addition, characteristics of combustion and NOx and SO2 emissions were evaluated through TG-DTG and TGA-FTIR. In the WT process, it was confirmed that the amount of NOx in the emission gas after combustion was reduced as a part of the fuel-N was decreased, and SO2 showed a similar value as a whole. Through this, it was confirmed that biomass after the WT process showed better performance than raw biomass in terms of combustion reactivity, emission gas, and ash.