In the present study, Ag nanoparticles modified Fe₃O₄ anchored on roughened halloysite nanotubes nanocomposites (Ag@Fe₃O₄/RHNT) with high peroxidase-like activity and good magnetism was fabricated, and accordingly, an efficient and sensitive colorimetric sensing platform was established for the detection of H₂O₂. Firstly, halloysite nanotubes was pre-treated and then Fe₃O₄ nanoparticles were uniformly deposited on the external surface of RHNTs. Finally, Ag nanoparticles were grown onto Fe₃O₄/RHNT by in-situ reduction method. All characterization results confirmed the successful synthesis of Ag@Fe₃O₄/RHNT. The resultant Ag-Fe₃O₄ RNHTs exhibited satisfied catalytic activity to the oxidation of TMB (4,4’-Diamino-3,3′, 5,5′-tetramethylbiphenyl) in the presence of H₂O₂, and the catalytic process is accompanied with the color changed from colorless to bule. Thus, a sensitive colorimetric sensor for detection of H₂O₂ was developed based on Ag@Fe₃O₄/RHNT nanocomposites. And the optimal reaction temperature and pH were determined to be 55 °C and 4, respectively. H₂O₂ can be detected in the range of 10–100 μM with the detection limit of 0.7 μM. In conclusion, we established an efficient colorimetric sensing system for H₂O₂, and applied it to detect H₂O₂ in milk and serum.