In this study, the structure of supercritical water (SCW) is investigated by Raman spectroscopy and molecular dynamics simulations. It was found that the hydrogen bonding in water is closely related to temperature and pressure (or water density). According to the Raman spectroscopic study of SCW, the existence of tetrahedral hydrogen bonds in SCW is also affected by the density of SCW. In addition, for SCW with critical density (0.322 g cm(-3)), we suggest that the tetrahedral hydrogen bonding is absent at water critical point (647 K and 22.1 MPa) based on Raman evidence. From the dependence of nu(max) of the Raman OH stretching bands on temperature and pressure, the structure of SCW can be divided into three-dimensional and chain (or string) hydrogen bonded networks, which correspond to liquid- and gas-like phases, respectively.