Abstract: The deviator strain energy density factor S_d is considered here as a fracture criterion for mixed-mode fracture.The criterion implies that the deviator strain energy plays a vital role during the crack propagation of metal materials,while the whole strain energy does not.Examples are provided to illustrate the application of the new criterion.The Ⅰ-Ⅱ mixed-mode crack initiation angle and the critical load are predicted successfully.The results gained using the present approach agree well with theoretical results and experimental data in the open literature.