Abstract: In this paper, the ionic hydration of five ions Li~+, Na~+, K~+, F~-, Cl~- is investigated by molecular dynamics simulation at 298.15K. A clear microscopic configuration of ions in aqueous solution is obtained. The cations are surrounded by water molecules with oxygen atoms approaching them, while the anions are surrounded by water molecules with hydrogen atoms approaching them. A new hydration factor is proposed to quanti tativelycharacterize the strength of ionic hydration. The order of hydration strength for cations is Li~+>Na~+>K~+, whereas for anions F~->Cl~-. For Li~+, although there is a second coordination shell, no second hydration shell exists. These are valuable information for further establishment of molecular thermodynamic models for electrolyte solutions.