Abstract Background Chinese herbs have been widely used for thousands of years. In order to kill or control insects and fungus during the cultivation of herb plants, pesticides have played a significant role. More than 30 kinds of pesticides have been documented in the latest version of Chinese Pharmacopoeia. It is urgent to develop new analytical methods for pesticide detection. Methods A fluorescent detection system was established by using Cerium based fluorescent polymer and Sm-CeO₂. As a new doped nanozyme, Sm-CeO₂ exhibits OPH-like activity to hydrolyze OPP pesticide. Results The morphology of the prepared CFP and Sm-CeO₂ were characterized. The optimal conditions for CFP synthesis are CeCl₃ (16 mmol L⁻¹, 200 μL), ATP (4 mmol L⁻¹, 200 μL) and Tris buffer (5 mmol L⁻¹, 500 μL, pH 8.0). Sm-CeO₂ shows the best mimic activity to hydrolyze OPP pesticide at pH = 8.0. The results exhibit good linear relationship between fluorescent quenching effect and MP in the range of 2–50 μmol L⁻¹. Finally, this fluorescent technique was successfully applied in Poria cocos and Semen Coicis sample. Conclusions It is the first report on OPP detection by using CFP and doped nanozyme. The successful application in real sample indicates this method is a rapid, reliable strategy to detect OPP in Chinese herbs.