Ultraviolet photoelectron spectroscopic(UPS) measurements of the tri (β-naphthyl) phosphine (TNP) film deposited on the Ag(110) surface were made. The TNP derived valence features are located at 38，63，93and 110 eV below Fermi level, and the top of the highest occupied molecular orbital(HOMO) of TNP is located at 25 eV in binding energy. The work function of Ag(110) is about 43 eV, and upon deposition of TNP, the work function decreases to the saturated value of 38 eV. Based on the UPS measurements, the energy level alignment at the interface of TNP/Ag(110) is given, and the results indicate a weak interaction between TNP and the Ag substrate.