The invention provides a method for preparing anti-interference paper reinforcing agent, comprising the steps as follows: (1) according to molar percentage, 80-96% of acrylamide monomer, 1-10% of double-bonded carboxylic acid monomer, 1-15% of water-soluble cation monomer and 1-5% of 2-acrylamide-2-methyl propane sulfonate monomer are taken and added in water while stirring to prepare a mixed water solution; (2) the pH value of the water solution is adjusted to 4.0-5.0; under the protection of nitrogen, the temperature is increased to 50-70 DEG C; subsequently, crosslinking agent, molecular weight regulator and prophase initiator are added so that the polymerization reaction is carried out for 20-35min; and (3) later initiator is added in the outcome in step (2), with the temperature kept within 80-100 DEG C for 30-60min; subsequently, termination agent is added so that the polymerization reaction is stopped. The method is stable and controllable, and can obtain the product which has strong anti-interference capability, high crosslinking degree, good flowability, complete copolymerization, low residue, uniform distribution of cations, and stable and controllable viscosity during the polymerization process.