The library is prepared through mRNA isolation (from total RNA), fragmentation, synthesis of cDNA, end-repair, adapter-ligation, size selection of library, and library amplification. Magnetic beads for sorting was used to get a specific-length library rapidly, meeting the personalized demands of different experiments. Three separate packages of NR1, NR21 and NR31, containing all enzymes and buffers required for library construction, have passed the quality control and function assay test , maximally promising a stable and repeatable output cDNA library.