Abstract: Dissipative particle dynamics(DPD) method was applied to simulate the selfassembly behaviors of PEO-PPO-PEO triblock copolymer in ethanol solution. The impact of volume fraction and PEO chain length on its mesoscopic morphology were investigated. In the ethanol solution with φF88=20%, the micelle changed from balanced disperse phase to regular transient phase as time went. Finally, a balanced cylindrical aggregate was formed using PEO as the core, PPO as the shell. Different kinds of mesoscopic aggregation types were observed with the change of volume fraction and the size of PEO chain length, for example like: spherical, cylindrical, threedimensional network, lamellar and perforatedlike structure. Results show that DPD method is an effective tool to study the mechanism of selfassembly of triblock copolymer and the formation of mesoscopic structure. It also plays important significance on the synthesis of special materials with desired properties.