The invention discloses a method for preparing poly(p-phenylene terephthalamide) (PPTA) in the technical field of the preparation of PPTA. In the method, p-phenylenediamine and terephthaloyl dichloride are used as polymer monomers; and liquid nitrogen is added in the polymerization process to solve the problem of removing the reaction heat. By analyzing the coupling of the polymerization process of PPTA, the direct transition heat-removing technology is utilized to solve the problem of removing a large quantity of released heat in the polymerization process, thus the overall temperature of the reactor can be uniform and the local temperature in the reactor can be uniform. By adopting the process coupling method, the entire polymerization process of PPTA tends to be milder, the heat transfer problem of the polymerization process of PPTA can be solved, the oxidation of monomer caused by the reaction heat of the polymerization process can be effectively improved and the molecular weight of the polymer can be fully increased. The entire polymerization process can be simple and practical and engineering scale-up is easy to perform.