A displacement method is provided to determine the stress intensity factors of nodes on crack surface in cracked body.The K I at the points along crack front of surface crack are obtained from the curve of KI versus r by the extrapolation.The KI of semi circular and semi elliptical surface crack in the finite thickness plates subjected to tensile load are calculated by the three dimensional finite element method.The photoelastic experiments with stress frozen method are made to examine the accuracy of the calculated results by the present method.Based on the expression proposed by Elber and Newman for the crack growth rate

the crack growth pattern and the life prediction of semi elliptical crack in a turbine disk of a jet engine are investigated.It is shown that the method presented in this paper is simple and convenient to analyse surface crack problems of engineering components.