Bitterness of peptide is caused by hydrophobic amino acids, associated with protein amino acid composition, degree of hydrophobic peptides, amino acid sequence and structure are important factors. Natural hydrophobic groups are contained within the molecular structure of the protein inside, so as to not appear bitter. When the protein into low molecular weight peptides would expose hydrophobic amino acid residues, which flirts with amino acid residues, appeared bitter. Large hydrophobic amino acid residues lysine, isoleucine, threonine, phenylalanine, such as hydrophobicity of amino acid residues in the peptide is higher, then the bitterness of peptide may be stronger. Hydrophobic amino acid residues in the c-terminal will result in bitter flavored strong addition to alkaline amino acid residues found will strengthen the bitter taste of peptides and the bitter taste of bitter peptides associated with specific molecular conformation, namely Rotary conformation of polypeptide chains at both ends of water formed, bitter when more powerful. But when the relative molecular mass of soybean peptides larger than 5000D there is no bitter taste, relative molecular mass 500~1000D the bitterness of soybean peptides is the strongest. With the decrease of molecular weight and bitterness gradually weakened.