The invention discloses a magnetically separated bamboo charcoal-based wastewater treatment agent and a preparation method and the application of the treatment agent. The saturation magnetization intensity of the treatment agent is 5-10 emu/g, and the specific surface area of the treatment agent is 90-130 m<2>/g. The treatment agent is prepared via the following steps: (1) cleaning bamboo charcoal, suction filtration, drying, breaking and obtaining bamboo charcoal powder; (2) weighting two or more types of transitional metal salts, adding deionized water, preparing and obtaining a mixed solution; (3) dispersing the bamboo charcoal powder into the mixed solution, ultrasonically and uniformly stirring, dropwise adding precipitant, depositing, regulating pH value to 7-10, heating, stirring at a constant temperature to react, standing, layering, pressure reducing, suction filtration, and obtaining a deposit; and (4) immersing the deposit in hydrochloric acid solution, suction filtration, scrubbing to neutrality, drying and sintering. The treatment agent is applicable to treatment of dye wastewater, fluoride wastewater, or heavy metal ion wastewater, is large in specific surface area, good in absorption performance, time-saving, safe, efficient, inexpensive, environmentally-friendly, economic, and simple in process, and can achieve continuous separation and recovery.