Abstract: Using sol-gel method to make the hydroxyl activated surface of nano Fe3O4 particles coated with amorphous TiO2, and the TiO2 coating layer was modified by doping polar molecular acrylamide to prepare Fe3O4/TiO2 core-shell composite particles. And then, the core-shell composite particles were distributed into methyl silicone oil to prepare composite particles electrorheological fluid. The phase and microstructure of composite particles, as well as the electrorheological characterization of electrorheological fluid were studied. The results show that TiO2 can be uniformly and intimately coated on the surface of nano Fe3O4 particles. When coating times were four, stirring time was 4 h, and mass fraction of acrylamide was 25wt%, the composite particles electrorheological fluide could obtained the best electrorheological characteristics, and its shear strength up to 41.9 kPa.