Abstract: The driving of water by natural gas in tight sands is an extremely a complicated process．The injecting of gas from the bottom of tight sands has the feature of piston-fashioned water driving when both porosity and permeability of the sands are homogeneous．The accumulation of gas will be typically source-contacting or root-sourced when the driving of water by gas is pistonfashioned, Typically，source-contacting gas or basin-centered gas will not be accumulated when the tight sands are of heterogeneous or even fractured ，since the piston-typed and replacement-fashioned driving of gas will occur in the same time．In this paper，we will discuss the accumulation conditions and equilibriums of source—contacting gas for typical and practical hypothesis．Conditions for the accumulation of source-contacting gases or rooting gases can be summarized into the regional existence of tight sands，abundant supplying of generated gas，directly contact between source rocks an d reservoirs，and integration of reservoirs an d seal rocks．As a result，the equilibrium equations for the formation of different types of source-contacting gases，or basin，centered gases are established respectively．Further more，the applications of equations is concisely discussed．The result indicates that the formation condition of typical source-contacting gas is not related to the height of gas column as in normal gas accumulation，instead，it is closely related to the buried depth．