In the paper a method is introduced, which had been used to measure radon emanation coefficients of coal samples from different regions in china. The influence of the size, water content and specific activity of coal sample on radon emanation coefficient is analyzed from results. The study show that the radon emanation coefficient is independent of specific activity of coal samples, increase when the size decrease and have a relation with water content, it decline along with increasing of the water content when water content...