The invention is a method for preparing magnetic grain-attapulgite nano composite, characterized in using attapulgite clay and iron salt as raw materials, by nucleation of bivalent, or bivalent and trivalent iron ions on the attapulgite surface and their stable action on crystal nucleus, caused by the attapulgite clay, directly crystallizing nano magnetic grains in solution, and depositing on the surface of the attapulgite crystals, so as to compose the composite. And it has super paramagnetism and strong absorptivity, able to be controlled under the action of magnetic field to implement magnetic flocculation, magnetic recovery, magnetic filtration, and target control of attapulgite sorbent. And it can be widely applied to the fields of purification of industrial raw materials, deep filtration for air purification, nano film material, deep processing for water supply processing, etc.