Abstract: Change of molecular magnetic moment of motherliquor and shear yield strength are studied in magnetorheological fluid.It is found from the study that   if magnetic induction strength is small,relative error of shear yield strength  linearly increases as magnetic induction strength increases,and it rapidy increase as electrons in molecule of  motherliquor increase.While the relative error hardly changes if magnetic induction strength increases to some value. In order to decrease error,molecule with less electrons must be as chosen as the motherliquor.

Key words: magnetorheological fluid, molecular magnetic moment, shear yield strength