The geometries and the electronic structures of t-HfO2 and its (001) surface have been studied by first-principle calculations using the density func tional theory (DFT). The optimized results show that the t-HfO2 (001) surface has no surface reconstruction. Compared with the bulk electronic struct ure, the density of states (DOS) of t-HfO2 (001) surface is higher th an that of the bulk. In addition, the DOS of t-HfO2 (001) surface is closer to the Fermi level. The valence band has the tendency to move toward the lower energy, resulting in the formation of a new surface state. The band gap of t-HfO2 (001) surface is much smaller than that of bulk band gap. The existence of a new surface state and the reduction of band gap are due to the r eduction of the Hf and O surface coordination which are different from the bulk atoms.