Ion hydration and its effects on water structure in different concentrations were studied using molecular dynamics (MD). The peak positions and intensity of radius distribution functions (RDF) of M+-Ow correlated strongly with the charge/radius ratio. And the coordination numbers of Na+, K+, Mg2+ and Ca2+ were 5.6, 6.7, 6.0 and 7.8, respectively. The ions' hydration structure including Cl- weakly depended on the counter-ions and concentrations. Moreover, ions primarily affected the structure and kinetics of ion's first hydration shell. As the concentrations increased, the RDFs for water slightly changed with decrease in the self-diffusion coefficients of water molecules and ions.