In this study, the effects of carbohydrates, proteins, and lipids on the combustion and pyrolysis characteristics of hydrochar were investigated by adding pure substances during hydrothermal carbonization (HTC) of typical food waste to magnify their effects on hydrochar. The experimental results demonstrated that carbohydrates enhanced the homogeneousness and thermal stability of hydrochar. Proteins showed minor effects on their combustion behavior. While the proportion of lipid in feedstock increased, its derived hydrochar exhibited a higher volatile content (74.51%), lower activation energy (101.1 kJ/mol), and more violent combustion process of hydrochar. An ingenious method of acetone leaching was applied to elute the attachments on the surface of hydrochar and further investigate their chemical constituent and influence mechanism of lipids. When the lipid content in feedstock increased during HTC, the attachments on hydrochar were verified to be dodecanoic acid and dodecylamide, which were the main chemical constituents of the volatile matter in hydrochar. They rapidly decomposed and burned at a lower temperature range (141-256 degrees C), resulting in the diminution of the ignition temperature (193 degrees C) and combustion activation energy. The results can offer referential information for improving the combustion and pyrolysis characteristics of hydrochar from food waste.