[en] Nano-phosphors YPO${}_4$:2%Sm${}^{3+}$ with different pH values were synthesized with hydrothermal method. The influence of pH on structure, morphology and fluorescence property of nano-phosphor was researched. The product composition, structure, morphology and luminescent properties were characterized and analyzed with X-ray diffractometry (XRD), scanning electron microscopy (SEM and EDS), infrared spectrometer (FT-IR), ultravoilet spectrometer (UV), fluorescence spectrophotometer (FL) and other instruments. The research results indicated that: the tetragonal crystal system structure of pure phase can be obtained at pH 1–5, and the mix phases of tetragonal and hexagon can be obtained at pH 7–9. The product morphology is fusiform at pH 1; spherical at pH 3–5; and bar-shaped at pH 7–9. As pH is gradually increased from 1 to 9, the fluorescence intensity of nano-phosphor is gradually decreased and then increased. The nano-phosphor with pH 1 has the maximum fluorescence intensity and fluorescence lifetime; moreover, it has better fluorescence thermal stability, and its activation energy is 0.233 eV.