The invention belongs to the technical field of materials and particularly relates to a method for preparing a carbon nano tube modified by boric acid or borate. The method comprises the following concrete steps: firstly, a carboxylcarbon nano tube reacts with diamine to obtain an aminated carbon nano tube; and then the aminated carbon nano tube reacts with the boric acid or the borate under the action of a catalyst to obtain the carbon nano tube grafted and modified by the boric acid or the borate. The method realizes the covalent grafting of the boric acid or the borate to the carbon nano tube. An obtained product has good dispersion in a high-performance resin matrix, can improve various mechanical properties, the thermal property and the friction property of the resin matrix, and realize the upgrading and updating to products such as a phenolic resin, bimaleimide and ethylene rhodanate or develop novel application fields.