Low-density hydrothermal vapor and vapor-like fluid occur widely in various geological environments from middle crust to terrestrial surface, and they are important agents for the transport and enrichment of ore-forming metals. Geologically significant tungsten contents or tungsten-bearing minerals are found in fumarolic condensates, sublimates and incrustations in volcanic areas and in vapor phase of fluid inclusion in ore deposits, showing tungsten can also be dissolved and transported in aqueous vapor. The solubility of tungsten in water vapor and vapor-like fluid in the WO3-H2O system was experimentally determined at temperatures of 350 ℃~400 ℃ and pressures of 60~200 bar, and whereby the influence of water vapor pressure on the solubility was investigated. The results indicate that the fugacity or contents of tungsten in water vapor are much higher than the vapor pressure of solid WO3 calculated with the volatile data in water-free system, demonstrating hydration takes place between the gaseous solute of tungsten and the solvent of water vapor, which promotes the dissolution of tungsten in the vapor. Based on thermodynamic analysis, the solubility is attributed to the formation of hydrated gas species WO3 · nH2O(g), and the hydration numbers are 1.4 at 350 ℃, 1.6 at 370 ℃, and 2.9 at 400 ℃, respectively. Thus, WO3 · 3H2O(g)or H2WO4 · 2H2O(g) and H6WO6(g) is likely to play an important role in the gaseous transport and concentration of tungsten in the magmatic-hydrothermal or pneumatolytic-hydrothermal circumstances such as porphyry system under high temperature and pressure conditions, whereas the complexes with less hydration numbers, WO3 · H2O(g)(or H2WO4)and WO3 · 2H2O(g)(or H2WO4 · H2O), whose proportion varies with the water vapor pressure, will probably predominate in the hydrothermal vapor at lower temperatures and pressures. Vapor-rich inclusions occur commonly in some porphyry and vein-type W(-Mo) deposits, the magmatic fluid dominated by low-salinity aqueous vapor exsolved from acid magma during crystallization is mostly responsible for the gaseous transport and gathering of tungsten and molybdenum in the apical space of the granitic pluton and overlying wall rocks. Subsequently vapor can evolve into metal-bearing high-salinity liquid or brine through condensation or further produce low to moderate salinity mineralizing fluid by mixing with infiltrating groundwater. Fluid boiling or phase separation caused by pressure drop and replacement and alteration in wall rocks will result in the deposition and enrichment of W, Mo and other metals in different stages and structural-lithologic positions.