It is stressed that the structure plays a decisive role on the property of materials. Materials generally with rigid molecular chains possess outstanding mechanical performances. However, this structure-property relationship is ambiguous in some polyimide (PI) materials. In this study, three typical homo-PI fibers, derived from pyromellitic dianhydride(PMDA)/p-phenylene diamine(PDA), PMDA/4,4-oxidianiline (ODA) and 3,3',4,4'-biphenyldianhydride (BPDA)/PDA respectively, were prepared by a two-step wetspinning method. The tensile strength and modulus of the BPDA/PDA PI fiber were higher than that of the PMDA/ODA PI fiber, while the PMDA/PDA PI fiber was too brittle to take the tensile test. Nevertheless, the rheology and dynamic thermomechanical analysis(DMA) results indicated that the rigidity order of polymer chain was PMDA/PDA > PMDA/ODA > BPDA/PDA. Accordingly, the chain conformations of different PI fibers were described by molecular simulation, and a molecular packing model was proposed to explain this structure-property contradiction. (C) 2018 Published by Elsevier Ltd.