To exploit an efficient technology to treat high strength wastewater by biogas fermentation, a laboratory-scale experiment were carried out to assess the performance of an anaerobic fixed-bed reactor (AFBR) packed with active carbon fibre as biofilm carrier for treating an acidic and high strength molasses wastewater. The continuous operation of the system was started using an initial chemical oxygen demand (COD) concentration of 5 000 mg/L at a hydraulic retention time (HRT) around two days. When the reactor was fed with COD under 47 000 mg/L, the relevant organic loading rate (OLR) was equivalent to 21.38 kg/(m3×d), the COD removal efficiency was above 86%, biogas and methane productivities of unit volume of 9.51 and 6.46 L/(L×d) were achieved respectively at that level. COD removal efficiency decreased respectively from 86.48% to 74.40%, 67.02% and 63.50% when OLR were increased from 21.38 to 35.13, 39.06 and 44.88 kg/(m3×d), and the relevant biogas productivities of unit volume were 13.71, 13.98 and 11.44 L/(L×d), and the methane productivities of unit volume were 8.84, 8.67 and 5.89 L/(L×d), respectively. Influent pH value of the AFBR was usually ranged between 3.5-5.6 without any pretreatment. Effluent pH value was ranged spontaneously on a feasible condition of 6.8-7.6 after methane fermentation. When the pH value was beyond the range of 6.8-7.6, the alkalinity was required to maintain the pH value at a suitable range. With the experiment progressing, a high strength influent COD of 78 600 mg/L was achieved, which was equivalent to an OLR of 44.88 kg/(m3×d). The anaerobic fixed-bed reactor presented an efficient treatment of acidic and high strength organic wastewater, and a strong anti-impact load capacity. The sludge production was so low that the reactor did not wall up in the process of 165-day operation. Therefore, it can save managing and economic cost.