The invention provides a charcoal and iron composite material and a preparation method thereof. The charcoal and iron composite material consists of carbon-base nano hydroxyl iron and microorganism which is immobilized on the carbon-base nano hydroxyl iron and has a capacity of degrading polluting inorganic salt in water, wherein the carbon-base nano hydroxyl iron is additionally composed of activated carbon and nano hydroxyl iron supported on the activated carbon, because the carbon-base nano hydroxyl iron can adsorb the polluting inorganic salt in the water, and specially domesticated microorganism having special degrading capacity on the polluting inorganic salt can rapidly degrade adsorbed and enriched polluting inorganic salt; therefore, the charcoal and iron composite material disclosed by the invention can organically combine a physical adsorption water purification method and a biodegradation water purification method when purifying water, so as to simultaneously adsorb and degrade the polluting inorganic salt in the water, thus greatly improving water purification efficiency.