In response to global warming, the world power plant plans to consistently phase out coal-fired power generation or replace coal with biomass such as wood pellets. However, when the biomass is used itself as a fuel, it is hard to be grounded because of the internal structure. To solve these problems of biomass the torrefaction is the one of the technologies which can enhances the grindability and energy density of the biomass. In order to confirming the utility of this biomass, the combustion characteristics should be analyzed, especially ash formation in the boiler. In this study, these characteristics according to the torrefied wood pellet blending ratio were analyzed using horizontal combustion reactor(HCR) and a scanning electron microscope with energy dispersive spectrometer (SEM-EDS). The SEM-EDS analysis could confirm that the initial ash deposition layer was formed predominantly by ash components had a significant effect on the growth of ash. Furthermore, the tendency of ash deposition with respect to torrefied biomass blending has been studied, along with discussions on the mechanism of ash deposition with the substances composing ash in blending cases.