The aim of this work was to study the correlation between dynamic mechanisms of carbon structure associated with their upgrading effects with the help of XPS, C-13 NMR and 2D-PCIS methods. Results showed the fuel qualifies of biowastes were improved and became comparable to lignite or even bitumite after HTC. The carbon chemical bonds of -C-H and -C-O in biowaste components (mainly protein and polysaccharide) were thermally cracked and enriched in liquid phase in the form of soluble intermediates, which subsequently generated coal-like structures via cyclization as well as polymerization at higher temperatures. The further investigation on thermogravimetric analysis found that the conversion of "-C-H/C-O to aromatic -C-C/C=C" was beneficial for stabilizing their combustion behavior by integrating two stages of biowastes (devolatilization stage and combustion stage) into one stage of hydrochars (combustion stage).