The Xiasai Ag polymetallic deposit is located at Chaluo Village, Batang County in Sichuan Province, and belongs to middle range of Yidun island arc orogenic belt in western Sichuan. It is a typical continental collision of Ag- polumetallic deposit that firstly discovered in China. The deposit is featured by highgrade Ag and associated with Sn, Cu, Bi, Cd, Au, with plenty of sulfides and sulfosalt minerals, about 50 species, especially diaphorite and tetrahedriteAg series which are the main ore minerals. Moreover, other sulfosalt minerals, such as geocronite(Sb), owyheetie- (Pb), boulangeritejamesonite series are also found. This study is focused on genesis of these sulfosalt minerals and figuring out their roles in mineralization. Analysis by EMP and SEMEDS indicate that these sulfosalt minerals are mostly included in galena or marmatite as inclusions, and chemical composition of them are analyzed. The grain size of diaphorite varies from 1μm to 50μm. It is interesting that diaphorite perform as orthogonal littice texture in galena which is rare found. In addition, other unique occurrences also appear. In order to estimate the temperature of the oreforming of the deposit, the value of Ag/(Ag+Cu) and Zn/(Zn+Fe) ratios of Ag- tetrahedrite series are ploted on sack’s isothermal curves, thus oreforming temperature of tetrahedriteAg series is assumed 200~350℃. Combining with former data of temperature measured by quartz inclusions, it is considered that the Xiasai deposit should be a post- magmatic mesothermal deposit. Briefly, the importance of metallization of sulfosalt minerals should be noticed.