Abstract: The tight sand gas is one of unconventional gas, it is also an important candidate resources of conventional gas.The opinion based on the research of predecessors.After fully thinking of the background of structural evolution,and dynamical analysis the relationships between the hydrocarbon genera-tion and expulsion fastigium of source rock and tight evolution history of reservoir,divide the tight sand gas reservoir into two types: "pre-exiting deep gas" and "subsequent tight sand gas".According to the comparative analysis on reservoir forming conditions,reservoir forming characters and reservoir forming principle of this two types,generalize the reservoir forming patterns and distribution regulation.The reservoir forming patterns of "pre-exiting" deep basin gas reservoir is divided into three kinds: depression central symmetry distribution,!foreland lateral margin slope distribution and structure slope distribution."first is the conventional accumulation,but late is reconstruction" is the reservoir forming pattern of "subsequent" tight sand gas,and the pattern is divided into three phases with different reservoir forming characters and conditions.Correctively distinguish the two kinds of tight sand gas from each other is very important to guide natural gas exploration and make the right exploitation plan.