In order to improve fuel quality of sewage sludge, fruit and agricultural wastes have been selected for hydrothermal co-carbonization. After hydrothermal co-carbonization, organics retention was facilitated, while O/C and H/C atomic ratios of hydrochars were substantially upgraded. Particularly, hydrochar from hydrothermal co-carbonization of sewage sludge with peanut shells at mass ratio of 1:3 (denoted as "SS:PS = 1:3") showed the highest fuel ratio of 0.79 and its carbon content was increased to 50.0% with significantly decreased O/C and H/C atomic ratios. Furthermore, higher heating value of hydrochars from hydrothermal co-carbonization was increased by nearly 2.65-fold and reached 21.72 MJ/kg. Moreover, the most favorable aromatization occurred when sewage sludge and peanut shells blending ratio was 3:1 or 1:1, whereas hydrothermal co-carbonization induced more CO and OH than COOH in hydrochars due to synergistic decarboxylation. A relatively higher value of point of zero charge for hydrochars from hydrothermal co-carbonization implied improved hydrophobicity. Combustion kinetics results indicated that hydrothermal co-carbonization balanced activation energies of hydrochars in devolatilization/combustion stage and char combustion process, rendering a more stable and lasting combustion profile. Hydrochars "SS:PS = 1:3" demonstrated desirable combustion performance. Therefore, hydrothermal co-carbonization can realize sustainable utilization of organic solid wastes towards superior hydrochar solid biofuels.