The invention discloses a modular improved iron-carbon microelectrolysis filler, a preparation method, application and assembly method thereof, belonging to the fields of water treatment and fillers. The method comprises the following steps: uniformly mixing scrap iron, common coke powder, copper powder, an adhesive and the like to form a mixture, putting the mixture on both sides of a wire net which is used as a skeleton, carrying out high-pressure compaction, sending into a furnace, and carrying out high-temperature calcination forming while charging protective nitrogen to obtain a modular improved iron-carbon microelectrolysis filler; and simply assembling the microelectrolysis filler units to form the modular improved microelectrolysis filler body. The improved microelectrolysis filler has the advantage of accessible raw materials. The microelectrolysis filler platy unit is simple in production method and convenient to assemble and use. The microelectrolysis filler does not have the phenomenon of hardening or blockage in the use process, and can be widely used in wastewater purification treatment engineering in printing, chemical industry, electroplating, coking and the like.