Nitrobenzene (NB) is toxic and resistant to biodegradation and widespread in surface water and groundwater. The persulfate (PS) system has been employed for the NB degradation and proved to be effective. Zero-valent iron (Fe-0) has been used for the activation of PS (Fe-0/PS) recently. However, the process exhibits a significant drawback of slow release of Fe2+ from Fe-0, resulting in low efficiency of the approach as Fe2+ is the primary species for the PS activation. In this study, a weak magnetic field was utilized to pre-treat Fe-0 for PS activation (pre-Fe-0/PS) based on the magnetic memory of iron. The efficiency of the pre-Fe-0/PS process was tested on the degradation of NB in simulated groundwater under anoxic conditions. The NB removal in the pre-Fe-0/PS process was significantly enhanced compared with that in the Fe-0/PS process. The effect of Fe-0, PS, and NB concentration on the NB degradation was investigated. The influence of single inorganic ions, anion couples and humic acids as ubiquitous species in groundwater on the NB removal in the pre-(FePS)-P-0 and Fe-0/PS processes were studied and discussed. A column filled with pre-Fe-0 was designed to test the NB removal in the pre-Fe-0/PS process in a continuous-flow mode. The experimental results indicated that pre-Fe-0/PS is a promising approach for the remediation of groundwater with high NB concentration.