Electrorheological (ER) fluids are one of the most important intelligent materials in the last century. Their rheological properties can be controlled by the external electric field. It is the suspension system of the high dielectric constant of solid particles dispersed in low dielectric constant liquids. The preparation, structure evolution and analysis of mechanism are the earliest research field in our laboratory. Many productions such as papers and patents have been worked out. At present, giant ER fluids with high dynamic performance are being developed and characterized.