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The contributions of different strengthening mechanisms to yield strength of bainite/martensite multiphase rail steel with different finish cooling temperatures in the controlled cooling process were quantitatively investigated. Dislocation density and substructure size of the rail steel were measured by scanning electron microscopy, electron backscatter diffraction and X-ray diffraction. The results show that the dislocation density increases with the decrease in block width in rail steel. Based on the correlation among dislocation density, block width and yield strength, a physical model was proposed to predict the yield strength of rail steel. The variation of block width and dislocation density in different positions of rail head microstruc-ture was integrated with temperature field simulation. Dislocation density and block width reveal significant correlations with the finish cooling temperature.