Abstract: This paper proposed an electromagnetic NDT method for inspection and characterization of railhead fatigue oblique crack using vertical magnetization. The characteristics of natural crack initiation and propagation induced by rolling contact fatigue (RCF) were analyzed and simplified for theoretical investigation of vertical magnetization test. The relationship between detection signals and crack dimensions, such as inclined angle with running surface, growth path with different turning angles, propagation depth and length of surface crack and buried depth of sub-surface crack, were provided by carrying out 2-D static FEM simulation. The results demonstrated that this approach could effectively recognize surface and sub-surface oblique crack and their propagation characteristics. This approach is suitable for rail RCF damage inspection and fault early warning of high speed railway.