Analysis of amino acid sequences can provide useful insights into the tertiary structures of proteins and their biological functions. One of the critical problems in amino acid analysis is how to establish a digital coding system to better reflect the properties of amino acids and their degeneracy. Based on the hydrophobic index, a one-to-one relationship has been established between the amino acid sequence and the digital signal process. Such a "bridge" will make it possible to apply all the existing powerful methods in the signal processing area to analysis of the amino acid sequences.