According to the core observation and statistics of physical properties, it is found that weathering, tectonism, lithology and litho-facies are the predominant factors of volcanic reservoirs in Carboniferous of Junggar Basin. The reservoir space includes primary fractures, primary porosity, secondary porosity and secondary fractures. The permeability is mostly controlled by fractures. Weathering crust is the main reservoir of volcanic rock in Carboniferous. High quality reservoirs are mainly located 250 m from the top of weathering crust. As the distance from the top of weathering crust increases, the filling degree of fractures as well as porosity becomes higher and this degrades the reservoir quality.