Two-dimensional thin tellurene (Te) was effectively synthesized by a one-pot hydrothermal reduction process. It had the hexagonal phase with good crystallization, the extent of radiation absorption (400-850 nm), and a 1.37 eV band gap. Based on the evolution of the crystal structure and morphology, the formation mechanism of Te nanomaterials has been speculated by the time-dependent reactions as the nucleation of nanosized clusters first, then self-assembly into uniform nanowires, and, finally, formation into the nanosheets in the presence of polyvinylpyrrolidone (PVP). It is expected that thin Te nanosheets can further be used in the field of photoelectric applications.