Dissipative particle dynamics (DPD) simulation method was performed to study the ethyl butyrate/ethanol/Tween80( Polysorbate 80)/water four-component microemulsion system. The dynamical process of microemulsion system formation was investigated. The microstructure and droplet shape changed with the water phase solubilizing was researched. The boundry of microemulsion's effective region was also predicted . The results of DPD simulation were as follows :(1) With the water phase solubilizing

the system's microstructure would be transformed at a certain water content which was 50% and 70% respectively and meanwhile

the shape of droplet transformed from columnar to sphere

then back to columnar and ultimately became sphere.(2) When the oil-surfactant volume ratio was or less than 5:5

water phase could be infinitely diluted; when the oil-surfactant volume ratio was 10:0

9:1

8:2

7:3 and 6:4

the maximum water content of microemulsion system was respectively 25%

30%

35%

45% and 50%

and microemulsion was water-in-oil. The water content of microemulsion was over the the maximum water content

it would be destroyed and layering. Experiments showed: (1) According to the changes of microemulsion system's conductivity

the microemulsion was water-in-oil when water content was less than 55%; the microemulsion was bicontinuous when water content was between 55% and 70%; the microemulsion was oil-in-water when water content was more than 70%. (2) The pseudo-ternary phase diagrams of system presented an effective region of microemulsion. The results of DPD simulation coincided with the experiment results.