Based on the classic static bending theory of a homogenous steel I-beam,the authors of this study investigated the load-displacement performance of non-homogeneous wood I-joists（IJ）made from different wood composites.The theoretical results and actual load-displacement data of wood I-joists were compared.The results indicated that:1)the classic static bending theory based on a steel I-beam could still be applied to wood I-Joists within the elastic stage;2)the tensile strain of the bottom flange and the compressive strain of the top flange were different and should be distinguished when designing wood I-joists.