The aminoacyl-tRNA synthetases (AARS) are very important during the protein biosynthesis, which can make the gene sequence be accurately translated into the protein sequence by the specific recognition between AARS and tRNA/amino acids. However, the recognition between AARS and tRNA/amino acids can be either specific or compatible, which is not only related with evolution of AARS structures, but also with the different evolutionary stage of life organisms containing AARS. AARS could undergo a evolutionary process from “ambiguous specificity” (multiple specificities )to “accurate specificity” (single specificity).