Abstract: Based on the method of Westergaard, the mode Ⅰ crack stress field is obtained for related boundary conditions. The tangent plane at the crack tip is used as the stress field area at the pipe crack tip. The mode Ⅰ crack tip stress field and its influence area are obtained, and the differences of the crack tip stress fields are shown between the pipe and the flat plate. The theoretical result shows that the influence area of the crack tip stress field is related to the crack length and the tensile stress.