This thesis studies the influences of additives on shear stress of electrorheologial fluid(ER fluid) in order to improve performance of ER fluid. ER fluid contains additives, and it is organic carboxylic acid(T1) or fatty acid and many entity mellow fat(T2,T3) .Then we test it. The result shows that all of the additives improve the performance of ER fluid. When the electric field is strengthened to 4 kV/mm under the condition that the content of additive is 3 percent, the shear stress of the ER fluid with different additive is improved in the rate of 12%,26%,33% respectively. The result also demonstrates that T1 contributes to a considerable increase in the stability of ER fluid. It is concluded that there will be a significant improvement in the property of ER fluid by dispersing appropriate type and a mount of additive to a certain ER fluid.