A novel magnetically tunable diffraction grating based on V-shaped and magnetic nanoparticles is proposed and demonstrated experimentally. The grating’s period we made was 10 µm, and the grooves and the convex groove were both 5 µm. The refraction index of the fer- rofluid is sensitive to surrounding magnetic field. We’ve demonstrated the magnetically tenability of this grating by measuring the changing of the diffraction angle of the high order diffraction light. The diffracted light was received by CCD and the movement of the laser spot, i.e., the small change of the diffraction angel was recorded. This approach is a good candidate for the following applications: magnetic sensors, magnetic controlled optical switches, modulator and so on.