The embodiment of the invention discloses a method for preparing a Ziegler Natta catalyst by taking a porous polymer microsphere as a carrier. The method comprises the following steps: reacting the porous polymer microsphere with alkyl magnesium chloride in a solvent to obtain a first reaction product; reacting the first reaction product with TiCl4 in the solvent to obtain a second reaction product; and allowing the second reaction product and a promoter to form the Ziegler Natta catalyst by taking the porous polymer microsphere as the carrier. In the method, the first reaction product which is the porous polymer microsphere with Mg-Cl bond is prepared by reacting the alkyl magnesium chloride with the porous polymer microsphere; the prepared first reaction product reacts with TiCl4 through the Mg-Cl bond to generate Mg-Cl-Ti bridged bond and obtain the second reaction product; and the promoter and the second reaction product form the Ziegler Natta catalyst by taking the porous polymermicrosphere as the carrier, and the promoter ensures that the second reaction product has the catalytic activity.