A novel zerovalen-iron-biochar composite (nZVI/SBC) was synthesized by using FeCl3-laden sorghum straw biomass as the raw material via a facile one-step pyrolysis method without additional chemical reactions (e.g., by NaBH4 reduction or thermochemical reduction). The nZVI/SBC was successfully employed as an activator in phenol degradation by activated persulfate. XRD, SEM, N2 adsorption-desorption and atomic absorption spectrophotometry analysis showed that the nanosized Fe0 was the main component of the 4ZVI/SBC activator, which was a mesopore material with an optimal FeCl3·6H2O/biomass impregnation mass ratio of 2.7 g/g. The 4ZVI/SBC activator showed an efficient degradation of phenol (95.65% for 30 min at 25 °C) with a large specific surface area of 78.669 m2·g-1. The recovery of 4ZVI/SBC activator after the degradation reaction of phenol can be realized with the small amount of dissolved iron in the water. The 4ZVI/SBC activator facilitated the activation of persulfate to degrade phenol into non-toxic CO2 and H2O. The trend of Cl-, SO4 2- and NO3 - affected the removal efficiency of phenol by using the 4ZVI/SBC activator in the following order: NO3 - > SO4 2- > Cl-. The one-step synthesis of the nanosized zerovalent-iron-biochar composite was feasible and may be applied as an effective strategy for controlling organic waste (e.g. phenol) by waste biomass.