The invention specifically relates to a block polymer with a high Flory-Huggins interaction parameter and for directed self-assembly, a random polymer, preparation methods for the block polymer and the random polymer, and a self-assembling method, belonging to the field of synthesis and application of high-molecular compounds. The block polymer is prepared through anionic polymerization, the Flory-Huggins interaction parameter among blocks is great, and compatibility is low. The random polymer is prepared through free radical polymerization of the monomers of the block polymer and epoxy methylacrylate monomers, and the random polymer is neutral to the blocks of the block polymer. The block polymer provided by the invention coats a cross-linked random polymer neutral layer and undergoes annealing heat treatment so as to form a phase separation structure perpendicular to a substrate, so production efficiency is improved, and a pattern with a size of 20 nm or below can be formed. The block polymer and the random polymer are applied to pattern transfer in the field of microelectronics, and process requirements and production cost are lowered.