A coal processing method includes adding coal powder, water and catalyst into a series of tandem reactors and processing therein, wherein the coal powder, water and catalyst are added into the first reactor of the series of tandem reactors; and the temperature and pressure of the series reactors is alternatively arranged in sub-critical state and supercritical state of water from the first reactor, the total product from the previous reactor is used as the feed of the next reactor without any further separation.