In this thesis,we investigated the electronic structures , bandstructures and Fermi surfaces of hexagonal tungsten bronzes Rb0.25WOy (RWO), by means of density functional method within a generalized gradient approximation to the exchange-correlection functional. W5dyz/zx was found to play an important role in charge transport properties. Our result also show a oxygen content induced significant change of carriers in RWO. Moreover, our calculated bandstructures and Fermi surfaces indicate the existence of electron (hole) pockets which may result in confined electron hole phenomenon.