A global crack-line displacement fitting procedure to extract the stress intensity factors (SIFs) is proposed in this paper. The proposed procedure uses the entire crack opening displacement (COD) data and its numerical calculation only involves in displacement fields. The post processing is greatly reduced and no new contour and remeshing are needed. The procedure can be easily applied to mixed mode crack problems with arbitrary crack shapes. In addition, the errors of the obtained SIFs can be estimated from the error information of COD data by this procedure. The procedure has been applied to several test examples of crack problems with their COD data being calculated by using a constant element boundary element method with two special crack tip elements. The results verified that the proposed procedure is reliable, accurate and easily implementing to extract SIFs.