Rare earth Tb3+ doped gadolinium phosphate (GdPO4) green phosphor is a potential phosphor for white LED, while the preparation by conventional hydrothermal method has some problems, such as long reaction time and low doping amount of Tb3+. A series of Gd1-xPO4∶xTb3+ (x=0, 1%, 5%, 11%, 13%, 15%, 17%, 19%) samples were prepared by hydrothermal method combined with high temperature sintering. The phase structure, morphology, elemental composition, optical absorption and luminescence properties of samples were characterized by X-ray diffractometer (XRD), scanning electron microscope (SEM)-energy spectrometer (EDS), infrared spectrometer (FT-IR) and fluorescence spectrophotometer. The results show that, all the synthesized samples are pure phase of GdPO4 belonging to monoclinic monazite structure, and the Tb3+ are uniformly distributed in GdPO4 matrix and cause lattice shrinkage. Under 274 nm photoexcitation, GdPO4∶Tb3+ phosphors have the strongest emission peak at 545 nm, which belongs to 5D4→7F5 transition of Tb3+. The fluorescence quenching concentration of Tb3+ was determined to be 15% (molar ratio), and this sample (GdPO4∶15%Tb3+) exhibits excellent green light emission and good thermal stability.