The invention aims at the characteristic of higher relative humidity of the flue gas of fire coal after spray drying, calcium spraying in a furnace, tail humidification, activation and desulfurization are carried out on the flue gas of the fire coal and provides a device and a method which apply a vapour phase change principle to realize the effective removal of SO2, also induce the coagulation and the growth of fine particle substances and remove the fine particle substances with high efficiency. The device for enhancing the removal of the fine particle substances in a flue gas desulfurization process of the fire coal comprises a desulfurizing tower or a humidification activator, an electrostatic dust collector, a flue gas reheater and a draught fan, wherein the electrostatic dust collector, the flue gas reheater and the draught fan are sequentially connected with the desulfurizing tower or the humidification activator by pipelines, a vapour phase change chamber is provided with a rinsing waste liquid outlet, a flue gas inlet and a flue gas outlet, the flue gas inlet is connected with a flue gas outlet of the electrostatic dust collector, the flue gas outlet is connected with the flue gas reheater, a vapour nozzle, a defogger and a rinsing water nozzle are sequentially arranged between the flue gas inlet and the flue gas outlet of the vapour phase change chamber, an inside lining of the vapour phase change chamber is provided with an anticorrosion material with low surface energy, and the anticorrosion material with low surface energy has double effects of increasing the phase change effect and preventing corrosion.