With a simple model for a surfactant consisting of a hydrophilic head group and hydrophobic tail groups connected by harmonic springs, the structural change of the association structures of the surfactant in an aqueous solution was studied by using the dissipative particle dynamics (DPD) simulation. The effect of the interaction parameter of DPD particles on the structural change of the association structures was also studied. Simulations show that the proper relative values of these interaction parameters could yield desirable changes for the association structure depending on the concentration of the surfactant. That is, a spherical structure forms at φ=0.15, structural change from a spherical to cylindrical one occurs at φ =0.26, and a hexagonal structure appears at φ =0.30, where φ is the volume fraction of surfactant SDS (sodium dodecyl sulfate), and they are in good agreement with observation.