Abstract: Tectonic system is the main factor which controls the accumulation of petroleum, and the local structures is the important prerequisite for oil preservation. The distribution of highly productive gas fields in Southern Szechuan is controlled by the "suitable" structure which is formed by the multi-system composite.The inheritant uplift in the ancient and modern tectonic systems is disadvantageous to petroleum preservation; the composite tectonic system,which is formed on the background of inharmonic depressions and slops, is favaorable for both petroleum accumulation and preservation.