In this paper， the phase behavior of Tween80/short-chained alcohol/ethyl butyrate/water microemulsion systems (MEs) were studied through the pseudo-ternary microemulsion phase diagram. The effects of different Tween emulsifiers， cosurfactants and mass ratios of surfactants and cosurfactants (Km) on the one-phased microemulsion areas and numbers of fully dilutable lines were investigated. And the microstructures and molecular interactions of microemulsions along the fully dilutable line L91 (the water content kept growing with the constant mass ratio of surfactants and oil phase as 9 ∶ 1) were characterized based on NMR techniques. The possible microstructure transition of W/O→ordered bicontinuous microemulsion phase→O/W→swollen micelles was inferred with the water content gradually increasing along fully dilutable line L91. Based the NMR selective 1D NOESY experiments， the interactions between different component molecules in the bicontinuous phase were suggested， that is the ethyl butyrate was trapped inside the lamellar structure in less touch with water. And the cosurfactant molecules may locate in both the interface and the water phase and interact with both water and ethyl butyrate. Tween 80 was absorbed in the interface. And its hydrophilic moieties get in touch with and interact the water and ethyl alcohol molecules while its hydrophobic moieties get in touch with and interact with the ethyl butyrate molecules.