The invention provides bamboo charcoal-based microelectrolysis porous ceramsite filler and the preparing method thereof. According to the filler, iron serves as the anode, carbon serves as the cathode, and the cathode carbon is made from bamboo powder. According to the preparing process, activation and carbonization of bamboo powder are integrated, bamboo powder also plays a role in partial pore forming, the filler is of a porous honeycomb ball-shaped structure, the grain size is 1 mm - 15 mm, water absorption is 20% - 45%, and the specific surface area is 30 m<2>/g - 60 m<2>/g; iron powder, bamboo powder, clay, activating agents, catalysts, pore-forming agents and binding agents are mixed evenly to form a ball, the ball is placed in a muffle furnace to be roasted, nitrogen is introduced into the muffle furnace for protection, the temperature is increased to 150 DEG C - 250 DEG C, pre-activation and pre-carbonization are conducted for 30 min - 60 min, then the temperature is increased continuously to 500 DEG C - 800 DEG C, heat preservation is conducted for 1 h - 3 h, then the temperature is naturally reduced to the indoor temperature, and finally the bamboo charcoal-based microelectrolysis porous ceramsite filler is obtained. According to the bamboo charcoal-based microelectrolysis porous ceramsite filler and the preparing method thereof, raw materials are environmentally friendly and easy to obtain, the preparing technology is simple, the filler has a good effect in sewage treatment and is suitable for heavy metal and dye sewage treatment, and the problems such as poor recycling property of traditional filler can be solved.