Based on 90 measured analysis data of formation water in Chang 4+5 & Chang 6 pay zone of Zibei⁃Zichang area, the features about type, chemical composition, pH, density, ion characteristic coefficient, salinity and planar distribution rule of formation water were investigated, and the implications of such features and hydrocarbon accumulation were revealed. Salinity of formation water of Chang 4+5 & Chang 6 pay zone is overall higher in this area, which has a neutral value in pH. The features conform general characteristics of sedimentary basin which has an increasing value with depth in vertical, and has a higher salinity with a closer distance to the center of the basin in planar. The density of formation water is logarithmically related to the salinity, which increases with increasing salinity. The main cation and the main anion are linearly related to salinity. Threshold is existed between K ⁺+Na ⁺ & Ca ²⁺ and salinity. Beyond that, Ba ²⁺+Sr ²⁺ & SO can coexist in formation water which is caused by the salt effect in it. The characteristic coefficient reflected by the formation water can effectively represent the accumulation and preservation conditions.