Dissipative particle dynamics simulations were performed to study the microstructures of doxorubicin (DOX) loaded/blank micelles self-assembled from cholesterol conjugated His(10)Arg(10) (HR20-Chol) at different pH conditions. DOX molecules can be efficiently encapsulated in the core of micelles. At pH >6.0, these micelles have stronger DOX loading ability due to the hydrophobicity of histidine residues, as compared to that of pH 6.0. With the decrease of pH from pH > 6.0 to pH < 6.0, the structure of micelles trends to be swelling from dense conformations. This structural transformation can facilitate the release of DOX from the core of micelles. All the simulation results are qualitatively consistent with the experimental results, demonstrating that the DPD method may provide a powerful tool in analysis and design of drug delivery systems.