A magnetic core shell Pr6O11/SiO2@Fe3O4 catalyst using chemical precipitation was prepared. Its structure was confirmed by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and energy dispersive X-ray spectrum. The catalytic activity was evaluated by the catalytic ozonation of acetochlor. The results showed that the catalyst could effectively improve the acetochlor removal and mineralization. The total organic carbon removal reached 37.3% with the catalyst at 120 min, whereas the removal was 14.1% with ozonation alone. The catalyst was proved to be stable and recyclable by determining the concentration of the leaching praseodymium ions and the catalyst's activity after repeated use. The effect of the radical scavengers indicated that the catalytic ozonation process followed an (OH)-O-center dot reaction mechanism. In addition, we employed Chlorella and zebrafish as model organisms to investigate the aquatic toxicity of the treated solution and the dissolved praseodymium ions. We found that the aquatic toxicity of the reaction solution decreased with an increase in the degradation time, and no obvious toxicity was found for the dissolved praseodymium ions.