Abstract: The NaHCO₃-typed water with the degree of mineralization up to 150g/L which is most highly mine ralized formation water in the Junggar Basin so far is discovered in the Carboniferous, the Permian and the Lower Triassic strata of the Fengcheng oil Field and the North Karamay Oil Field in the Karamay oil region on the northwest edge of the Junggar Basin. The first chemical characteristic of water is high boron (B) content up to 1700-2300mg/L which has not been reported at home and abroad. The second one is very high CO₃^2-+HCO₃^- content which makes up 56%～88% of the total anion content in the water. Of which, the CO₃^2- content is up to 31-39g/L, HCO₃^- content to 14～36g/L, and the re1evant Ca²⁺ and Mg²⁺ contents are all less than 0.1g/L. The crude oil produced simultaneously with high-mineralized NaHCO₃-typed water has greater change with density of 0.789～0.895g/cm³. This high pressure water rises from within along faults and is mixed with early formed CaCl₂-typed water to result in middle-high mineralized Na₂SO₄-typed water which is seen in the paleo-edge-water region of the Permian and Triassic oil accumulation in No.8 area. The high-mineralized NaHCO₃-typed water is inferred to generate when high pressure and high concentration CO₂ gas of unknown genesis comes into water in the deep of the crust. The distribution of discovery points suggests that it may have something to do with the deep buried faults and is consistent with the distribution of light crude oil (with density 0.84g/cm³) on the whole.