After qualifying the total RNA samples, according to the different characteristics of the mRNA, because eukaryotic mRNA has the structure of polyA tail at the 48' end, the magnetic beads with oligo (dT) are used for enrichment and purification; for prokaryotes, the mRNA doesn't have this characteristic, and the kit is used to remove the rRNA to obtain more effective information, and the Fragmentation Buffer is added to the purified mRNA to make the fragment more efficient and effective. Fragmentation Buffer is added to the purified mRNA to fragment it into short fragments, and then the fragmented mRNA is used as a template to synthesise the first strand of cDNA using six base random primers, and buffer, dNTPs, RNaseH and DNA Polymerase I are added to synthesise the second strand of cDNA, which is purified and added to the PCR kit using QIAQuick PCR. The second strand of cDNA was purified using the QIAQuick PCR Kit and eluted with EB buffer. The eluted and purified double-stranded cDNA was then subjected to end repair, addition of base A, addition of sequencing junctions and then recovered by agarose gel electrophoresis for target-sized fragments and PCR amplification, completing the entire library preparation.