The effective dielectric constant εliq of magnetic fluid is related to the volume fraction P of the magnetic nanoparticles and the factor α∥ of magnetic field. The changing relation of water-based MnFe2 O4 nanoparticle magnetic fluid effective refractive index with the volume fraction of the magnetic nanoparticles P and the factor of magnetic field α∥ was caculated. It was found that by adjusting α∥, the magnetic fluid has the same effective refractive index in difference of volume fraction of the magnetic nanoparticles. The transmission spectrum of doping one-dimensional water-based MnFe2 O4 magnetic fluid photonic crystal, when P is 0.745 and the structure is (AB)8C(BA)8, is numerically simulated by transfer matrix method. The results indicate that the wavelength of defect mode shifts to the side of long waves as increasing of nanoparticle magnetic fluid effective refractive index nc. That is, the wavelength of defect modes increase as increasing of nc. The amount of redshift is 36.6 nm. The quality factor of defect mode was disscused. It’s found that half of the peak bandwidth λw is a constant. The quality factor of defect mode Q and the wavelength of defect mode λ have the same characteristics of linear with the change of nc. That is, Q increases with the increasing of nc.