The Xialong Pb-Zn-Ag deposit is located in the west of the Gangdise porphyry Cu-Mo metallogenic belt and occurrs within the large granite batholith. It is a cryptoexplosive brecciated Pb-Zn-Ag deposit. In this paper we report the analytical results of the fluid inclusions and H-O-S-Pb isotopes. The ore-forming fluids in the Xialong deposit were evolved from high temperature (240~340℃), low salinity(2.2%~3.8% NaCl eqv) to low temperature(160~180℃), low salinity(0.8%~1.7% NaCl eqv). Analytical results of fluid inclusions show very low δD values. The δD-δ18OH2O diagram shows that ore-forming fluids originated from the mixing of magmatic and meteoric water. δ34S values of metal sulfides from this deposit range between -3.0‰~+5.9‰, with a small change range. According to extrapolation of isotope equilibrium coefficient, δ34S of metal sulfides gives two positive high average values of sulfur isotope, and the values of Σ34S are +9.80‰ and +13.13‰. Two positive-high Σ34S values reflect that ore-forming magma may have undergone degassing when evolving. The lead isotopic composition of metal sulfide is characterized by enrichment of radiogenic lead isotopic. 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb values of galena are 18.627~18.758, 15.598~15.682 and 38.637~39.298. 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb values of pyrite are 18.639~18.678, 15.587~15.691 and 38.649~38.703. These data show parts of ore lead enrich radiogenic lead, reflecting the multiple sources of lead and mixing of the upper mantle and upper crust lead. Our study reveals that magma associated with mineralization of Xialong Pb-Zn-Ag deposit comes from the partial melting of the lower crust, with mixing of mantle materials, and in the process of intrusion emplacement, also occurs magma mixing with the magma chamber in the upper crust. These also show that there may exist ancient crust in the area, which provides specific instructions for prospecting in the southern Lhasa terrane.