An important feature of membranes is the ability to control the passing rate or components within mixed species, which is highly dependent on the microstructure of membranes. That's why scientists have done a lot of research on the factors influencing the Morphology of the membranes and were trying to control it. The aim of this study was to investigate the rheological behavior and phase behavior of a ternary system consisting of water/DMF/PVDF and how they interact in influencing on the Morpholgy of produced membranes. In surveys, the characteristics such as: component of the polymer solution, the MFI of polymer that used in the solution, casting temperature and casting method was used to control the phase behavior and rheological behavior of the system. in order to do correctly survey on interaction between the rheological behavior and phase behavior, prepared conditions that the rheological behavior was constant while the phase behavior was variable, or reverse mode. The effect of the solution component on the morphology showed, rheological and phase behavior are vying for control the membrane structure. So that the phase behavior of system is the dominant and has a larger share in the control of structure. Investigation of the effect of polymer MFI's showed, in wet casting method, By changing the behavior of the system from a Binghamplasticto pseudoplastic, macrovoides increases and spherical particles size is reduced.the effect of phase behavior variation while the rheological behavior was constant, characterized by themperature and casting method. For polymer whit high MFI in the wet casting method, as temperatures rise, Rheological properties does not vary but the phase behavior changes. The difference in phase behavior results in increased macrovoids, also, due to the increase of the space thickness increases. By changing the casting methode for dopes whit same rheological properties, phase seperation path Changes. This provided a favored condition for liquid-liquid demixing in wet castin methode to take place and thus cellular morphologies were produced and the new picks were appeared in cristalization curve. Keywords : PVDF membrane, Ternary phase behavior, Rheological properties, porosity, nanostructure