Abstract: Formation water vertical characteristics are complex in Langgu sag,Jizhong depression.The vertical distributions of the formation water chemic and dynamical belts have obvious zoning features.According to the vertical characteristics of the formation water chemic and dynamical belts and the relations with fluid compartment and distribution of oil and gas in Gu'an-Jiuzhou,Liuquan-Caojiawu and Hexiwu tectonic belts,it is considered that formation water can be divided into four belts vertically.They are formation water alternate fluency belt,formation water alternate blocking belt,formation water alternate tardy belt and formation water frequency alternation belt.It is also considered that formation water alternate blocking belt tallies with fluid compartments and is the beginning segments of oil and gas enrichment.Meanwhile,formation water alernate tardy belt basically locates under the fluid compartment and it is the favorable area of oil and gas enrichment.Furthermore,the area with relatively high value of salinity in the lower salinity beckground is available to oil and gas enrichment.