Zhundong coal, rich in the Alkali and Alkaline Earth Metal elements, causes severe ash deposition during the combustion in many power plants. In this paper, the influence of vermiculite, as an additive, on ash deposition formation and the corrosion phenomenon caused by ash deposition are investigated in a drop tube furnace system. The formation process of ash deposition under real working condition can be simulated in this furnace system. The results show that vermiculite has a significant inhibition effect on the formation and growing process of ash deposition, as well as the corrosion phenomenon. At the beginning of ash deposition, the swelling vermiculite can effectively absorb the SO2 in the flue gas, which restrains the formation of Na2SO4 in the inner ash, close to the surface of heat exchangers. The mineral in internal inner ash gets changed and the phenomenon of corrosion on the heat exchangers surface gets alleviated. Meanwhile, the external inner ash presents with loose structure instead of the molten condition, which lowers possibility for ash deposition to grow. In outer ash deposition, close to the flue gas, the content of layered particles with high melting point, as Mg2SiO4, increases and viscous particles, like Ca2Al2SiO7, are separated from each other by the force of the vermiculite swelling. As a result, adding vermiculite makes it hard for ash deposition to form and grow. According to the experiments, with more than 5% blending ratio of vermiculite, the vermiculite additive has a positive effect on restricting the ash deposition.