Salt plays an important role in giving saltiness and adjusting taste in daily life. However, excessive intake of salt will cause certain harm to the body. Therefore, it has become an urgent need to develop new food processing strategies to reduce salt without reducing saltiness. In present study, Maillard reaction was employed to improve the flavor of Katsuwonus pelamis hydrolysates (KPSPs) with saltness. The change of flavor was measured by electronic tongue and sensory evaluation. After Maillard reaction of KPSPs and xylose, the bitter and other unpleasant flavor of the hydrolysates were reduced, whereas the saltiness and acceptability were enhanced significantly. The content of bitter amino acids of the Maillard reaction products of KPSPs (M-KPSPs) was reduced. Due to the covalent bonding between the peptide chain and the sugar molecules, the intrinsic fluorescence intensity was weakened with a redshift of the maximum emission wavelength, indicating that the tryptophan microenvironment became looser and more hydrophilic. The decrease in the composition of bitter amino acids and a change in the secondary structure of the peptides might lead to the change in the perception of flavor. The findings suggested that Maillard reaction affected the flavor characteristics, which provided a new idea for the improvement on non-Na+ saltiness of healthy food additives via Maillard reaction between protein hydrolysate and reducing sugars.