Abstract: The author researched the reservoir diagenesis and organic inclusion in the reservoir,Bajiaochang gas field.In this area,the fluid inclusions distributed chiefly in dissolved seams and pores in quartz grains and not in secondary quartz margin and structure slot.Their diameter was under 0.5μm,the abundance was not up to 5% their phases had chiefly gaseous hydrocarbon adding brine and single gaseous hydrocarbon and their homogenization temperature peak was between 100~120℃.In the forth interval gas reservoir of Xiangxi Group,gas charge started from late period of the Middle Jurassic and a large number of fluid inclusions were formed in the accumulation was formed from the Upper Cretaceous to Xishan Epoch when the formation stopped gradually.