RNA extraction from cells was used TRIzol™ (Invitrogen™ 15596026) and Direct-zol™ RNA Miniprep(zymo R2050). 0.2ug of total RNA was used for the construction of  sequencing libraries. Based on the structural characteristics of polyA tail in most mRNA of eukaryotes, the mRNA with polyA tail was enriched by Oligo(dT) magnetic beads. Then, according to the process of library building kit, the first strand of cDNA was synthesized using fragmented mRNA as template and random oligonucleotides as primer, then the RNA strand was degraded by RNaseH, and the second strand of cDNA was synthesized using dNTPs as raw material under the DNA polymerase I system. After the purified double-stranded cDNA was end-repaired, A tail was added and a sequencing joint was connected, cDNA of about 150-200bp was screened, PCR amplification was performed and PCR products were purified again, and finally a library was obtained.