Yield　stress　of　Electrorheological　(ER)　fluid　is　one　of　the　main　performance　coefficients　in　application　of　engineering.　So　based　on　the　rheology　theories,　the　change　laws　of　static　yield　stress　and　dynamic　shear　stress　with　shear　rate　have　been　researched　by　our　lots　of　experiments.　The　research　result　in　this　paper　shows　that　the　different　kind　of　ER　fluid　behaves　different　yield　performance　especially　in　the　conditions　of　both　post-yield　and　higher　shear　rate.　From　the　behavior　form　of　ER　effect　by　experimental　investigation,　the　expressions　of　static　yield　stress　and　dynamic　shear　stress　with　shear　rate　have　been　defined　respectively　and　the　relation　between　dynamic　shear　stress　and　static　yield　stress　also　been　investigated.　Both　the　highest　negative　and　positive　deviation　values　have　been　got.