Abstract: The elongation, compression and shearing characteristics of ER fluids under external electric fields are investigated. The compressive strength of ER fluids is found to be about one order higher than shear stress, and is 2~3 times of tensile strength. The compressive modulus is proportional to the square of electric field. The relationship between tensile yield stress and shear yield stress verified the credibility of the calculation model employing a yield angle shaped between particles. From the tested strength, the yield angle is found to be between 15°~18.5°, according with other reports well and verifying the validity of the calculation through particle shift in traditional theoretical analysis.