In this study, the authors have developed a software system based on influence function method using 3 D-FEM input data and 3 D-FEM result to improve prediction ability of fatigue crack growth analysis of surface cracks which initiates from root of boxing fillet welded joints of ship structures. The software system developed in this study uses the database of influence coefficients, K_ij , developed by one of the authors, Shiratori, for various types of surface crack through a series of FE-analyses. It is shown that crack growth result based on influence function method using 3 D-FEM result is more accurate for experimental data than the result by a method based on linear approximation of arbitrary distributed stress. And further study, a simple approximate equation of arbitrary distributed stress in the cross section of virtual crack surface are determined to simplify crack growth analysis based on influence function method. Surface crack growth analysis based on influence function method using the approximate equation gives almost the same result of that based on influence function method using 3 D FEM result.