Experiments on Sn transportation by vapors and related ore forming mechanism about orebody No100 in Dachang Tin orefield. There is a large orebody No.100 in the famous, Dachang Tin ore field. This orebody exhibits an irregular form distributed within more than 1200m in length. The ore formations can be divided into two stages: early stage of cassiterite sulfides, and late stage of cassiterite Pb/Sb sulfide sulfosalt. Fluid inclusion data from minerals indicates that in the early stage, at 300~400℃（450℃）, high salinity fluid inclusions coexist with the low salinity fluid inclusions. Those data demonstrate that the ore bearing supercritical fluids progressively entered in to L V two phase immiscibility field boiling phenomena were present. In the late stage, the variation in salinity is small, and temperature deceases continuously. The orebody No 100 occurred at temperatures 300 to 360℃, and pressure at 8.24MPa. This study designed L V immiscibility field experiments, in which Sn bearing super critical fluids fall in the subcritical states, and focused analyzing Sn redistribution between vapor and liquid phases as entering in L V two phase immisciblity field. The experiments are non equilibrium processes. Experiments mainly concentrated on analyzing the L V separation in + the V L two phase immiscibility field as a supercritical fluids （Zn） NaHCO3 HCl H2O entering to sub critical state at pressures 25~22MPa and 8~14MPa，at temperatures from 380~300℃. The experiments are isobaric processes and decreasing temperature. Results indicate that the L V separation of NaCl H2O occurred in the sub critical states of the Sn NaHCO3 HCl H2O. As far from the critical point, Na and Cl distributed in vapor and liquid, Na (V/L) and Cl (V/L) are progressively less than 1. It shows that Na and Cl mainly distributed in liquid phase. Those facts demonstrated that metal redistribution between vapor and liquid phases occurred, and Sn redistributed between L and V phases. Sn (V/L) is always much larger than 1. Sn is distributed in a poor NaCl, H2O CO2 vapor phase. At temperatures from 380~250℃, H2O CO2V L two phase immiscibility field occurred in the NaCl H2O CO2. Experiments found that in the L V separation processes of H2O CO2, HCO-3and CO2-3are weakly distributed in vapor phase, and mainly distributed in liquid phase. CO2 is rich in vapor phase. Sn is redistributed between in liquid and in vapor phases, and is rich in vapor phases.Experiments demonstrated that ore precipitated rapidly in the large cranny as it rapidly opened, then forming large orebody No 100. At temperatures from 300~360℃ and at low pressure (8.24MPa), ore forming fluids entering L V two phase immisciblity field, the vapor phase bearing Sn, Zn etc., transported rapidly and ores precipitated quickly.