Composite magnetic fluids were obtained by doping silicon dioxide and polystyrene nonmagnetic microspheres into the pure ferrite magnetic fluids. The relationship between the magnetic-field-induced birefringence of composite magnetic fluids and the species, concentrations of nonmagnetic microspheres and pure ferrite magnetic fluids were investigated qualitatively. The results indicate that pure magnetic fluids with different concentrations doped with equal quantity of polystyrene microspheres have different variation trends for the birefringence with respect to the externally magnetic field. Different kinds of nonmagnetic microspheres have different influences on the change of birefringence after doping into the same pure magnetic fluids. When doping with two-kind-mixed nonmagnetic microspheres (equal quantity but different proportion between the two kinds of microspheres), one kind of the nonmagnetic microspheres will play a leading role in the variation of birefringence with externally magnetic field. Then, the variation trend of the birefringence with externally magnetic field for the as-prepared composite magnetic fluids is similar to that only doped with the leading nonmagnetic microspheres.