In this study,food-grade microemulsions were prepared with tween-80 as the surfactant phase(S),ethanol,propylene glycol and glycerol were used as the co-surfactant phase(CS) and soybean oil,medium chain triglycerides and ethyl butyrate were the oil phase(O).The factors,including different oil,co-surfactant and conditions that affecting the formation of microemulsions were studied by producing pseudo-ternary phase diagrams.Microstructure and structural transition of the food-grade microemulsions with tween-80 were studied by detecting their conductivity and viscosity.The results indicated that the structure of oil and co-surfactant and the modification of temperature,salinity and pH acidity did influence the formation of microemulsions.Water in oil microemulsions were formed with the water contents below 50 wt.% to 56wt.%.Oil in water microemulsions were formed with the water contents above 70 wt.% to 72wt.% and bio-continuous microemulsions were formed with the water contents between 50 wt.% and 72wt.%.More surfactants were capable of increasing the structural transition from W/O structure to a bio-continuous structure and delaying another structural transition from a bio-continuous structure to a O/W structure,which eventually led to enlarge the formation zone of bio-continuous microemulsions.