Abstract: To obtain more crystal and magnetic structural information of powder crystals，magnetic field is introduced into X'Pert-MPD XRD apparatus with the strength of 0. 42 T and two different directions：one direction of magnetic field is vertical to the sample holder and another is parallel. XRD patterns in situ magnetic field are obtained for six samples which are representative of paramagnetic，diamagnetic，ferromagnetic，ferrimagnetic，antiferromagnetic substances and reduction product of FeCl2 by NaBH4 respectively. Compared with XRD patterns obtained in the zero magnetic field，there are some diffraction peaks disappear，some occur，or some diffraction angles and counts change. In addition，the patterns are different under the different direction of magnetic field. The cause is that magnetic dipoles in crystals are oriented along with the direction of magnetic field. The oriented magnetic dipoles produce stress in crystals and make crystal lattice changed（such as magnetostriction）or even turn particles aligned along with the direction of magnetic field to form preferred orientation of particles.