The invention provides a biological purification carrier for treating wastewater. A preparation method of the biological purification carrier comprises the following steps: firstly, mixing pretreated attapulgite with MBAA (methylene bisacrylamide) in saline water, and then stirring at the temperature of 50 to 70 DEG C for 1 to 3 hours; secondly, mixing a bio-polymer solution with the mixed solution, heating the mixed solution to 40 to 60 DEG C, adding activated sludge accounting for 2 to 5 percent of the mass of the attapulgite and nano iron-manganese composite oxide accounting for 1 to 3 percent of the mass of the attapulgite, adding a carbon nano tube accounting for 2 to 5 percent of the mass of the attapulgite, and carrying out stirring treatment at the stirring speed of 5 to 10r/min for 1 to 3 hours; thirdly, adding a cyclodextrin composite solution into the mixed solution, and then stirring at the temperature of 20 to 30 DEG C for 20 to 40 minutes, standing at the temperature of 10 DEG C for 30 minutes, then adjusting the temperature to be minus 5 DEG C to 7 DEG C, keeping the temperature for 40 to 60 minutes, carrying out slow stirring, curing and cross-linking, and then wrapping a mixture with gauze and squeezing out water, and washing the mixture with 10 to 20 percent tannin acid solution for 2 to 3 times; finally, putting the mixture into a baking oven at the temperature of 50 to 70 DEG C and treating for 8 to 10 hours, thus obtaining a finished product. According to the biological purification carrier for treating the wastewater, disclosed by the invention, the efficiency and the capacity of wastewater treatment can be effectively improved.