Abstract: The simple relationship between ω, β and the hydrostatic stress by using theory of slip line field was gained. According to the results of three-dimension FEM computation, the distribution of hydrostatic stress at crack tip has been obtained, the reason about the influence on the decrease of hyfrostatic stress of shallow notch has been analyzed, and the reasonable viewpoint of β and ω in analysis of slip line field has been verified. A new method is provided for theory analysis of shallow crack on the elastic-plastic fracture.