A new equivalent domain integral of the interaction integral is derived for the computation of the T-stress in nonhomogeneous materials with continuous or discontinuous properties. It can be found that the derived expression does not involve any derivatives of material properties. Moreover, the formulation can be proved valid even when the integral domain contains material interfaces. Therefore, the present method can be used to extract the T-stress of nonhomogeneous materials with complex interfaces effectively. The interaction integral method in conjunction with the extended FEM is used to solve several representative examples to show its validity. Finally, using this method, the influences of material properties on the T-stress are investigated. Numerical results show that the mechanical properties and their first-order derivatives affect the T-stress greatly, while the higher-order derivatives affect the T-stress slightly. Nakamura and Parks [19] and Wang [20] used the method to solve the T-stress along threedimensional (3D) curved crack fronts. Jayadevan et al. [21] employed the method to evaluate the T-stress in dynamically loaded fracture specimen. Sladek and Sladek [22] and Kim et al. [23] utilized the interaction integral method for computing the T-stress of an interface crack.Functionally graded materials (FGMs), as one of the representative nonhomogeneous materials, have many advantages that make them attractive in potential applications, such as the improvement on residual stress distribution and mechanical durability. introduced the interaction integral method to compute the T-stress of 2D cracks in isotropic and orthotropic FGMs and gave a summary on the definitions of the auxiliary fields. Using the method, Shim et al. [27] conducted an investigation on the elastic and elastic-plastic fracture problems of FGMs. Sladek et al. [28] used the interaction integral method combined with a meshless method and to evaluate the T-stress in orthotropic FGMs. Recently, the interaction integral method was used for the evaluation of the T-stress in isotropic and orthotropic FGMs under thermal loading [29,30].Most of the previous work is concerned with materials with continuous and differentiable properties. Actually, there exist more or less material interfaces in various nonhomogeneous composite materials and thus, the material interfaces have to be taken into account when the fracture performance of these composites is focused. In addition, FGMs are actually two-phase or multiphase particulate composites in which material composition and microstructure vary spatially or the volume fraction of particles varies in one or several directions [31]. Therefore, in certain scales, the material interfaces should be investigated when we examine the fracture performance of FGMs. In previous works [32,33], the authors have given an effective interaction integral method for extracting the SIFs in the materials with complex interfaces. The aim of this study is to develop an interaction integral method for solving the T-str...