The invention discloses a carbon-doped fiber filter cloth for removing mercury in a coal-fired flue gas and a preparation method thereof. The carbon-doped fiber filter cloth comprises the components of PPS fiber and active carbon powder in a weight ratio of 1 to 1, wherein the active carbon powder is adhered to the surface of the fiber in a fusion mode to form uniform adsorption active sites to heavy metal mercury in the filter cloth. The preparation method is conducted on an opening and cleaning system, a carding system, a needling system, a drying system, a spraying system, a thermoforming system and an active carbon powder spraying system. The carbon-doped fiber filter cloth has high temperature resistance and high strength, and particularly has a comparatively significant effect in adsorbing and removing the heavy metal mercury in the coal-fired flue gas; besides, the preparation method is simple and feasible, has a low cost and is easy for large-scale industrial production.