Water is the most important environment of lives.In this paper, the effect of aqueous environment on the supramolecular structure of DNA has been investigated by means of single molecule force spectroscopy (SMFS).On one hand, the small energy cost of the water rearrangement upon the duplex formation ensures the stability of dsDNA in the aqueous environment.On the other hand, by shaving off the water molecules binding to the duplex, dsDNA is destabilized and tend to be unwound.The weak intermolecular interactions involved in duplex formation seems to be handled carefully by a delicate "design" of the molecular structure of DNA, so that the self-assembly between the ssDNA chains can be reversible under a facile regulation These findings may explain, on the molecular level, why DNA is suitable to be the gene carrier.