The gelation process in Polyacrylonitrile (PAN)/Dimethyl Sulfoxide (DMSO)/Water (H2O) systems was studied by rheology. Chambon-Winter criterion was used to detect the critical gelation temperature variation. Interestingly, we found that the loss tangent coincided at two different temperatures in different frequency periods with the temperature decreased. By using the physical and mathematical analysis, we were able to tell that the first one was the critical sol-gel transition temperature, which appeared at higher temperatures under lower frequencies; and the second point was an indication of another self-similar structure, which appeared at lower temperatures under higher frequencies. We analyzed the coarsening mechanism in the gelation process of ternary blends, and considered that the volume growth of the physical linkage can interpret this unusual phenomenon. A 'Joint Point to Joint Section' model, similar to nucleation process, was proposed to interpret the mechanism of the growth of the physical linkages. Based on the above data, phase boundaries of critical gel and the second self-similar structure can be drawn. As the PAN or water content increased, both transition temperatures increased, which indicated the non-solvent water favored the aggregation of PAN molecules and promoted the forming of the second self-similar structure. (C) 2015 Elsevier Ltd. All rights reserved.