In this paper, we investigate surfactant aggregation at solid/liquid interfaces using a molecular dynamics (MD) simulation with a simple description of molecules and interfaces. To begin with, we verify that the simple model can capture, at least qualitatively, the basic characteristics of water/solid interfaces and micellar solutions. Thereafter, we simulate the surfactant aggregation on the smooth hydrophilic walls in micellar solutions. The mechanisms of the surfactant adsorption and aggregation are proposed on the molecular level, and how they are influenced by the concentration and structure of surfactant molecules is discussed in detail.