Abstract: A dual two-scale method was presented for computing 3D st ress fields of unidirectional-fibre reinforced composites considering the interphase. In the prediction of properties, the homogenized inclusion was obtained by homogenizing the fibre and the interphase, and the macroscopic homogenized material was obtained by homogenizing the homogenized inclusion and the matrix. In the characterization of 3D stress fields, by twice stress transmissions, the stress fields of the unit cell and the stress concent ration area were obtained in turn by the two-scale asymptotic technique. Combining with the finite element method, the 3D stress fields of the proposed composites, which are under the macroscopic axial uniform tensile load, were computed by the dual two-cale method. The numerical results show that the maximum stress occurs within the region which is in the middle section of each fibre and close to the border between fibre and interphase. The influence of different interphases on the distributions of stress fields was also discussed. The results show that arithmetical transition of the properties of fibre, interphase and matrix is beneficial to releasing stress concent ration.