Abstract: Peierls-Nabarro model is used to study the effect of magnetic fields on a straight edge dislocation.The Peierls-Nabarro force is calculated according to the model.The result shows that,in the presence of an external magnetic field,the Peierls-Nabarro force decreases for paramagnetic dislocations.This suggests that the plasticity of specimen can be increased because paramagnetic dislocations are easier to move in an external magnetic field due to the decrease of the critical shear stress.The result is consistent with the known magnetoplasticity effect.