During the translation process, aminoacyl tRNA enters the ribosome, decoding the codon on the mRNA and brings the mRNA moving forward towards the 5′ direction of mRNA, until the de-acylated tRNA leaves the ribosome, it moves through the ribosome in one direction. Recently, with the finding and identification of the highly conserved protein LepA, a new kind of tRNA movement inside the ribosome, namely the back-transloation of the tRNAs and mRNA in the direction of mRNA 3′ is discovered. With the in-depth research, the physiological meaning behind the back-translocation for the translational efficiency and fidelity has been studied.