The invention aims to provide a method for separating monomer n-alkanes from C11 to C25 from Fischer-Tropsch synthesis hydro-refining oil. According to the method, the Fischer-Tropsch synthesis hydro-refining oil is fed into one or more first rectifying towers and second rectifying towers which are arranged in parallel to be separated, so that the target monomer n-alkanes are obtained. According to the number of to-be-separated target products, the corresponding amount of rectifying devices are established, the process of separation is simple and flexible, device investment is small, the technology is flexible to operate, and technological difficulty is low; through the method, the high-purity monomer n-alkanes can be obtained through separation, additional value is high, and a good cost-income ratio is realized.