Abstract: Modified semi-analytical method (MAM) was created by applying the concept of differential and rule of composite ply stiffness distribution, which can be used to predict adhesive stress for scarf joints in composite structure. Firstly, validation of MAM was studied through the models of different ply angles and number of plies with finite element method (FEM) 2D plane strain. Then, the load carrying capacity of the composite scarf joints was predicted with average shear stress method, FEM and MAM. At last, MAM was used for analyzing engineering applications which concerned scarf joints with dissimilar modulus of adherends and variation of adhesive thickness. The comparison of results of these methods with the test values demonstrates that MAM is appropriate for designing scarf joints in composite structures, and the peak value of adhesive stress can be obtained with MAM and stress distribution is in accord with FEM calculation.