The Beilekuduke tin deposit occurs in syenogranite. According to mineral association and their occurrence, type of mineralization can be classified into three types: (1) altered granite type; (2) greisen type; and (3) quartz vein type. 40Ar/39Ar dating was performed on muscovite from greisentype tin ore, which yielded two plateau ages of 306.8 ± 2.4 Ma and 309.7 ± 2.4 Ma. Two plateau ages are coincident with the age of (306 ±5) Ma from Beilekuduke syenogranite pluton in error range. These plateau age data not only accurately reflect the timing of ore formation but also indicate the close relation between syenogranite and tin ore. Two types of fluid inclusions, namely NaCl—H2O and NaCl—H2O—CO2—CH4 types, have been recognized in quartz from tin ore. Homogenization temperatures of fluid inclusions in tin oreforming stage mainly vary from 160 to 250 ℃ and 280 to 390 ℃, with two peaks temperature of 210 ℃ and 330 ℃. Salinity ranges from 1.22% to 7.86% NaCl eq. Ore fluid densities range from 0.55 to 0.96g/cm3. The δ18OSMOW values of quartz from ore range from 9.6‰ to 14.1‰, with corresponding δ18OH2O values of 1.56‰ to 8.09‰, and δD values of fluid inclusions of between -128‰ and -95‰. The combined isotopic data imply that the oreforming fluids of the Beilekuduke tin deposit were mainly derived from magmatic fluids, with some minor contributions from meteoric water. Changes in physicochemical conditions and water — rock exchange and immiscibility of CO2—CH4 and NaCl—H2O in hydrothermal fluids are inferred to have played important roles in the oreforming process of the Beilekuduke tin deposit.