Objective: This study aimed to solve the problems of low freshness, heavy bitterness, and poor flavor of protein peptides hydrolyzed by enzymes of Harpodon nehereus （HN）. Methods: Ultrasound assisted enzymatic hydrolysis method was used to prepare the HN protein peptides. Papain was selected as the catalyst to study the changes in particle size, hydrolysis degree, soluble peptide content, relative molecular mass distribution, free amino acid content, and electronic tongue flavor signal of the HN protein peptides under different ultrasound power （0, 120, 240, 480, 600 W）. The effect of different ultrasound intensities on the structure and flavor of HN protein peptides was studied. Results: Under the control of the conditions of ultrasound intensity of 360 W, ultrasound time of 1 h, water bath temperature of 55 ℃, and water bath time of 4 h, the protein hydrolysis degree reached 19.29%, and the soluble peptide content was 0.57 mg/mL. Ultrasound assisted significantly reduced the particle size and relative molecular mass of HN protein peptides, and the proportion of components <3 000 increased from 67% to 82%. In addition, the bitter amino acids dominate the protein HN protein peptides, followed by sweet and fresh amino acids. The increase in the content of fresh free amino acids in the products of ultrasound assisted enzymatic hydrolysis was the largest. Therefore, ultrasound assisted enzymatic hydrolysis reduced the bitterness of HN protein peptides by increasing the content of fresh amino acids. Conclusion: Ultrasound assistance can enhance the enzymatic hydrolysis of HN proteins, thus improve the physicochemical properties and flavor characteristics of HN protein peptides.