Abstract: In order to understand the effects of different processes on the nutritional quality and flavor characteristics of fish head soup, this experiment used the bone and flesh mud of the head of the leather catfish as the raw material, used ordinary boil (OB) and ultrasound-assisted ordinary boil (U-OB), enzymatic hydrolysis (Eh) and ultrasonic-assisted enzymatic hydrolysis (U-Eh) four processes to prepare four groups of fish head soup, and nutrition, GC-MS, GC-IMS, and electronic nose were analyzed. The test results showed that the water-soluble protein content of ultrasonic-assisted treatment (U-OB) was significantly higher than that of the non-ultrasonic treatment group (OB); The calcium content and selenium content in the Eh and U-Eh groups were higher compared with OB and U-OB; The amino acid content of Eh and U-Eh was much higher than that of OB and U-OB, but the content of bitter amino acids was higher than that of umami and sweet amino acids. Taurine, carnosine and other substances were also detected in fish head soup. The results of the electronic nose showed that the odors of the four fish head soups were clearly distinguished, and there was no overlap. The U-Eh flavor profile was far away from the other three samples, and the flavor was relatively rich; GC-IMS technology identified 33 substances, mainly aldehydes and ketones. Compared between OB and U-OB and between Eh and U-Eh, their volatile organic compounds (VOCs) were similar in type but different in content. The common VOCs among the four groups of samples were only nonanal (dimer), 2-heptanone and nonanal (monomer), all of which had a good modification effect on the flavor of fish head soup.