The invention belongs to the field of chemical industry process, and especially relates to a system for preparing aromatic hydrocarbons from coal, and a method thereof. The system is composed of a water coal slurry gasification and purification unit, a coal gasification conversion unit, a synthetic gas distribution unit, a methanol synthesis unit, a methanol aromatization reaction unit, a vapor-liquid-liquid three phase separation unit, a light hydrocarbon separation unit, a dry gas separation unit and a dry gas conversion unit. The system separates dry gas generated in the aromatization process as a byproduct, converts the dry gas to produce synthetic gas, allows the synthetic gas to undergo gas distribution in order to produce methanol, returns the produced methanol to the aromatization unit in order to reduce coal consumption, and returns wastewater generated in the methanol aromatization reaction to the water coal slurry gasification and purification unit in order to prepare coal water slurry. The method can greatly reduce the coal consumption of production of unit of aromatic hydrocarbons, and also solves the utilization problem of the byproduct dry gas. The method is highly safe to operate, and the system has the advantages of high production strength, high operating flexibility, continuous process, less investment, low energy consumption, and suitableness for large-scale operation.