According to the EST sequence in cDNA library in our lab, the full-length cDNA sequence of AMP gene was cloned in the triangleshell pearl mussel Hyriopsis cumingii by the RACE-PCR. A 970 bp cDNA sequence contained a 123 bp 5′-untranslation region, 526 bp 3′-untranslation region and 300 bp open reading frame(ORF), which encoded 99 amino acids with a signal peptides of 27 amino acids and a mature peptide of 72 amino acids, and molecular mass is 10 924.7 u. Amino acid sequence analysis shows that in the sequence there exist an obvious transmembrane and a hydrophobic region. Homology analysis indicates that this full-length amino acid sequence showed the highest similarity with Aplysia californica theromacin (56%), lower similarity with defensins,mytilins,myticins and mytimycins in mussels, so it is speculated that this gene belongs to theromacin gene families of antibacterial peptides. The prediction results of Jpred3 software for H.cumingii AMP protein secondary structure show that the places of 2-22, 57-62 amino acid residues had the alpha helix, accordingly, AMP in H.cumingii is the membrane protein containng transmembrane spiral. This study may lay the molecular basis for further research on the gene expression, function and disease defense of H.cumingii.