The invention relates to a preparation method of a copolymer with a ferrocene-containing side chain, and belongs to the technical field of high polymer chemistry. The preparation method comprises the steps of preparing a ferrocene copolymer monomer; performing after-treatment for the ferrocene copolymer monomer; and copolymerizing and performing after-treatment again to obtain the copolymer with a ferrocene-containing side chain. According to the preparation method, the monomer can be synthesized by the one-step method, so that the cost is low, the reaction is mild, the operation is simple, and the separation and purification are simple; the processes are simply that feeding a large amount of water, filtering and then recrystallizing, without column chromatogram separating; therefore, the quality of the final product is easily controlled, and as a result, the stability of the final product quality can be ensured, and the demand of raw medicine production can be met; and the prepared polymer is simple to synthesize and outstanding in performances.