Abstract: In order to further study the mechanism of the electromagnetic radiation of coal,the atomic force microscopy (AFM) was used to study the distribution rules of electric parameters such as micro-surface potential and charge den- sity of coal samples with different metamorphism grades. This research pushes the study in this field to a micro-nano scale. The results show that the coal surface shows weak electricity at the meso-or macro-level or electrical neutrality, but exhibits certain electrical characteristics at the nanoscale. The surface charge density of coal samples varies from 79. 95 μC / m2 to 312. 97 μC / m2 ,and the difference of which is obvious. The metamorphism grade has an important in- fluence on the electrical parameters of coal surface:with the increase of metamorphism grade,the negative surface po- tential of coal undergoes a slow change first and then rapidly,while the surface charge density shows a “ V” curve change that firstly decreases and then increases. It is of significance to study the micro-electrical characteristics of coal and rock for further revealing the electromagnetic radiation mechanism,gas adsorption and desorption processes,and even the physical properties of coal from the micro level.