High-sulfur petroleum coke (HSPC), that is a by-product from slag oil in the coking process of refining, shows versatility values in practical applications and, however, concentrates the majority of organic sulfur. Herein, we design and construct a highly effective CTAB@HPA composites to be explored for the catalytic oxidative desulfurization of HSPC under mild conditions using hydrogen peroxide as the oxidant and 1-butyl-3-methylimidazole tetrafluoroborate ionic liquid as the extractant. The results demonstrate that the sulfur content of HSPC could be strikingly reduced from 4.46 wt% to 2.48 wt% under 60 °C and atmospheric pressure, and that the organic sulfur in HSPC is mainly oxidized to sulfoxide, sulfone and sulfate, which latter can be directly separated from petroleum coke. Moreover, the effect of reaction conditions on the desulfurization performance of HSPC as well as the catalytic oxidation reaction kinetic of HSPC desulfurization was systematically investigated. Furthermore, a mechanism for the oxidative desulfurization of HSPC over CTAB@HPA catalysts was proposed. Therefore, this work provides new insight into how to construct active catalysts for the desulfurization of HSPC under mild conditions.