Abstract: The reservoir-forming system research is the inevitable product of petroleum geology from static,qualitative to dynamic,quantitative description.Deep natural gas system is divided into 3 reservoir-forming dynamic systems such as normal pressure gas reservoir system of remote source,superpressure gas reservoir system of proximal source and inorganic reservoir-forming system,according to spatial location of source rocks,distribution characteristics of capping bed,reservoir pressures and mechanisms of migration-accumulation of natural gas in the northern part of Songliao Basin.There are K₁q^1-2-K₁d² assemblage with gas accumulation closed by K₁q^1-2,K₁d²-K₁yc assemblage closed by K₁d²,K₁yc-Jhs¹ assemblage closed by itself.Superpressure gas reservoir system of proximal source is a favorable direction for large-scale and medium-sized natural gas reservoirs exploration.