Abstract: The wide range variation of composition of formation water distributed in the different areas of the Taihe oilfield are likely to represent the different and complex system of fluid.Using the mapping of ion related parameters of formation water distribution in the Taihe oilfield,authors have tried to define forms and boundary of formation water system and determinate the direction of petroleum migration based on the gradient of ion related parameters.It is concluded that the distribution in the Taihe oilfield water shows a distinctly "Block form" along the N-S direction and "Zone form" in the E-W direction,i.e.,the Triassic formation water in No.1 and No.2 district of the Taihe oilfield is taken shape in E-W direction,and the "Zone form" of distribution of formation water in No.3,No.4,No.6 and No.8,as well as the Northwest part of No.7 are significantly present in the N-S direction with different variation tendency along theirs E-W wing,while the Southern platform in the Taihe oilfield suggests that variation of distribution from southeast to northeast and southwest.Besides,the distribution of formation water is locally present as isolated and closed fluid flow system in the shapes similar to cavern,barrel and other irregular forms,and it also have been found there are either intermediated zone between weak and strong water-flow movement or stagnate zone,the direction of petroleum migration is mainly interpreted as controlled from south or southwest to north or northwest in the Taihe oilfield in terms of the major ion concentration and its combined parameters.