Abstract: Based on the statistics and analysis of the testing results of formation water samples from the Shan 2 Member of Shanxi Formation in North Yulin, it's known that the formation water of destination layer is mainly acidic and the high mineralized, CaCl₂ water type, showing well closed condition of formation water. This formation water is located in the reductive block-stagnation hydrogeology condition, which is conducive to the accumulation and preservation of natural gas. The study of relationship between hydro chemical characteristics and natural gas reservoirs shows that it has a better correspondence with natural gas enrichment area among the total high mineralization degeree of the formation water, the distribution range of CaCl₂ type water, the low value area of rNa⁺/Cl^- (<0.5) and rMg²⁺/Ca²⁺ (<0.1), as well as the high value area of r(Cl^--Na⁺)/2Mg²⁺ (>10)l.