Porous carbon materials with ultra-high specific surface area and adjustable pore structure characteristicswere prepared from food industry waste hazelnut shells for the adsorption of methylene blue (MB)wastewater by two-step activation by impregnation with ZnCl2 followed by chemical activation withKOH. The Fusso effect, which can reduce the size of MB molecules, was further used to enhance theadsorption of MB on porous carbon. The results show that both HSBC-a and HSBC-a-b have ultra-highspecific surface area (2979.59 m2/g for HSBC-a, 2882.73 m2/g for HSBC-a-b). The mesopore ratio ofHSBC-a-b (Vmeso/Vtotal % = 14.05%) was doubled compared to HSBC-a. It showed an excellent adsorptionperformance of 694.03 mg/g for MB. It showed a fast adsorption kinetics and the adsorbed amountincreased to 882.46 mg/g at 0.1 M NaCl solution. In addition, adsorption processes were studied usingadsorption kinetics and adsorption isotherm model fitting. The results of this research confirm that hazelnutshell is a kind of promising and sustainable porous carbon raw material, and its ultra-high specificsurface area and adjustable pore structure characteristics are favorable for the efficient treatment ofMB from dyeing wastewater. This work could provide potential guidance for the high-value utilizationof waste hazelnut shell biochar.