The first neighbor distance rNa-O is estimated to be between 0.234 and 0.250 nm from experiments,but computer simulations suggest shorter values,varying from 0.224 to 0.239 nm.The account for an uncertainty as far as hydration number of Na+ is concerned,placing it between 4 and 8 and the general concept of sodium being a “loosely hydrated” ion is described.Second hydration shell around the sodium ion in aqueous solution is also described but with even greater ambiguity.The hydration structure of most common sodium ion with such a sophistication and controversy was really incomprehensible.In present paper,the hydration of sodium ion was reconsidered in both micro-hydration and bulk hydration aspects.