The coagulation process of polyacrylonitrile (PAN) precursor during wet-spinning was studied by chemical method based on the KMnO4 titration. Experiments were performed with gelled solutions of PAN in dimethyl sulphoxide (DMSO) to determine the diffusion rate of solvent during the coagulation. The experimental datas about solvent diffusion coeffecient were calculated by using diffusion equation, which reflected the coagulation process of nascent fibers. At the same time, the effects of coagulation on the residual solvent content, the change of morphology of nascent fibers, the crystallization degree and the stress-strain curves were studied by use of X-ray diffraction, SEM, single fiber tensible test and so on. The results elucidated the relationship between coagulation process and the structure and property of PAN nascent fibers.