Abstract: The change of longitudinal hydrodynamicconditions can have great effects on the migration and accumulation of formation liquid. The relatively stagnant environment with weaker hydrodynamic force is advantageous to the preservation of gas and oil. On the contrary, the relatively open environment with stronger hydrodynamic force is disadvantageous to the preservation of gas and oil. In this paper, the hydrochemical section types of Cainan area and Shixi area as well as the hinterland and southern edge of the Junggar Basin are analysed using formation water's salinity, water type, ratio of Na⁺ and Cl^-, and coefficient of desulfurization. The result reveals that the characteristics of positive type hydrochemical sections are shown in whole area, but reverse type and multi type sections do exist in some regions; there exists regions with stronger hydrodynamic force in deep strata with weaker hydrodynamic force and exists regions with weaker hydrodynamic force in shallow strata with stronger hydrodynamic force, and this is advantageous to the preservation of gas and oil; either positive type or reverse type or multi type hydrochemical sections, the preservation of gas and oil will be better provided the salinity of formation water is high and the change of sections is slower, otherwise the preservation of gas and oil will be bad if the change of sections is strong.