Abstract: Differences on organic/inorganic structures and fuel properties between sewage sludge-derived hydrochar and different-rank coals were investigated and compared with the help of FT-IR, XRF and XRD technologies. Meanwhile, the combustion behavior under various blending ratio and its synergistic effects was identified via TG and deviation analysis. The results demonstrates that the organic structures and combustion behaviors of hydrochar are similar to those of coals, which not only improves the combustion properties of sewage sludge, but also enhances the synergistic effects in co-combustion of hydrochar and coals. During the co-combustion process, light volatiles and (alkaline) alkaline-earth metals in hydrochar could accelerate the weight loss rate for coals, reaching 4.4%-16.1%, 1.9%-9.4% and 4.8%-12.1% for lignite, bitumite and anthracite, respectively. In general, the blends with 30% hydrochar and 70% lignite or 50% hydrochar and 50% lignite are better than other blends in terms of comprehensive combustion evolutions.