Abstract: In order to study the flowing characteristics of the Electro-Rheological fluid（ERF）in the gap of flat plates by macroscopical method, an electrorheological fluids is compounded, and the apparatus is designed too. The theoretical analysis of the fluid mechanics on the flow of the electro-rheological fluid in the gap of flat plates is carried out. The equation relating the pressure ΔP of the gap, flux Q and electric field intensity E applied on the gap of flat plates is presented. The experimental and theoretical results are compared with each other. With the increase of flux, the error between the experimental and theoretical results is increased. The factors affecting the error are discussed.