Ionic liquids (ILs) have been used in an enormous number of chemical and biological processes. In recent years, self-assembly of ILs into the micelles has attracted much attention and proved to be the key feature in interpreting many physical phenomena and have influence on fluids transport. Micelles or aggregates are mostly reported to be quasi-spherical objects with the alkyl tails forming the core and the imidazolium headgroups exposed to water. In this work, the formation and structure of rodlike micelle in [C(12)mim]Br aqueous solution was studied by molecular dynamics simulations based on the united-atom force field. Several separate simulations were performed using both liquid droplet and random-like starting conditions, and self-assembly of cations into the rodlike micelle was observed, which is consistent with the TEM result. A more detailed analysis and comparison between the solution and neat IL using radial distribution functions demonstrate the influencing factors of the micelles, the structure, and interaction between ions and water. Besides, the intermolecular energy and hydrogen-bond number and pattern were also analyzed to further reveal the nature of the micelles.