The invention belongs to the technical field of microbial carrier preparation methods and relates to a preparation method of a modified montmorillonite-containing reticulated polyurethane microbial carrier with an interpenetrated network structure. The preparation method comprises adding vinyl polyether polyol, polyether polyol, polyester polyol, H2O, silicone oil, a tin catalyst, an amine catalyst and an olefin monomer into a reactor, carrying out stirring to obtain a uniform mixture, adding modified montmorillonite into the mixture, carrying out stirring to obtain a uniform mixture, carrying out thermal insulation, wherein the mixture is used as a component 1, adding isocyanate and a free radical polymerization initiator into a reactor, carrying out stirring to obtain a uniform mixture as a component 2, mixing the component 1 and the component 2 to obtain a uniform mixture, carrying out foaming to obtain polyurethane flexible foam and carrying out meshing treatment on the polyurethane flexible foam through an alkali liquor immersion or explosion method to obtain the reticulated polyurethane microbial carrier with an interpenetrated network structure. The olefin polymer is introduced into the reticulated polyurethane microbial carrier through the interpenetrated network structure so that hydrolysis resistance and biodegradation resistance of the carrier are improved and compatibility of the polyurethane ingredient and the olefin polymer ingredient is improved.