Abstract: Central mud manipulation structure belt of Yinggehai Basin lies in centers of Yinggehai depression, enriches gas resource, includes several sets of regional combination of reservoir and seal, along with a bath of large scaled mud-manipulation anticline traps. Being its extra geological qualities, special oil gas reservoir come into being extensively over the mud diapiric structure belt. The DF gas well lies on the belt, where the mud manipulation is comparvetly weak and it's diapers isn't obvious. But there are extra conditions and reservoir formation system which make well DF1-1 become large scared gas reservoir:extreme thickness depositions, the vertical existation of several sets of combination of generation reservoir and seal, the activation of high thermal necessary. All become the necessary condition of the DF1-1 gas field.