Abstract: The stress and strain situations of the X70 pipeline with single spherical corrosion defect which was different in depth ( both the defect depths and the defect radii were t/8, t/4 and t/2 respectively, t is pipe wall thickness) were analyzed by finite element method (FEM) under different service conditions (inner pressures) . The Von Mises equivalent stress distribution and the Von Mises equivalent strain distribution at different conditions were obtained. And the stress concentration factor was calculated according to the FEM results. The results showed that in dead loading the stress concentration factor of corroded pipe with defect depth of t/8, t/4 and t/2 were 2.52, 3.43 and 7.16, respectively. Meanwhile the fitted equation of stress concentration factor and ratio of defect depth was established, and the correlation coefficient was 0.994. Besides, the results of stress concentration factor based on the FEM coincided with the results of similar references, which proved the correctness of the FEM.