The influence of two methods of gas moisture conditioning on removal efficiency of PM2.5 from coal combustion with addition of atomized droplets and steam was investigated. The particles size distribution and number concentration were measured in real time by electrical low pressure impactor (ELPI). The results show that collection efficiency of PM2.5 from coal combustion can be highly improved with steam condensational enlargement. Particle stage collection efficiency increases with the particles, especially for those smaller than 0.3 microm. The separation efficiency can be improved by 60% with the size of particles increasing from 0.03 microm to 0.3 microm for 0.1 kg/m3 of steam addition. The removal efficiency is independent of the gas temperature at the inlet of conditioning chamber for steam addition. But it increases with the gas temperature obviously for atomized droplets addition, which can be improved by 30% with increasing gas temperature from 136 degrees C to 256 degrees C. High removal efficiency of PM2.5 from coal combustion can be obtained with atomized droplets evaporation in hot flue gas except for steam addition.