<正> The electric conductivity, dynamic modulus and yield stress of the developed electrorheolo-gical fluid （ERF） are measured at different volume fraction and different electric field strengthusing a modified Rheometrics Mechanical Spectrometer （Model 605）. The percolation theory isintroduced to explain electrorheological effect and found that the ERF′s have the similarpercolated network structure as that of other ordinary suspensions with a critical volume fractionvalue independent of electric field strength. A master curve of dimensionless modulus againstdimensionless volume fraction is obtained. which shows that the essence of ER phenomenonactually is one kind of the second ofder phase transition.