A transformation route was developed for the conversion of raw corncob into furfural by a Cl-bearing solid acid catalyst (HSC-SO3H) prepared by the hydrothermal carbonization and sulfonation of sucralose. The catalytic performances of HSC-SO3H in selected solvents were demonstrated and optimized, where a furfural yield of 90.8 mol% (20.9 wt%) was achieved at 448 K in 30 min in gamma-valerolactone/water system. Interestingly, significant furfural yields were also obtained from cellulose. The effect of elevated temperature on furfural yield from high initial feedstock loading was also investigated. HSC-SO3H with -COOH, phenolice-OH, and -Cl as binding sites and -SO3H as the catalytic site on its surface presents a bifunctional catalyst, and synergic effects of these functional groups, reaction solvent property and temperature are made responsible for the good catalytic performances. The catalytic strategy proposed in this study demonstrated an effective transformation of corncob into furfural with a high yield.