The formation water salinity of Wumaying buried hill, a continuous deep buried hill in the southern part of Huanghua Depression, is generally high, indicating that the formation is well sealed. It is worth noting that the formation water of the Permian Lower Shihezi Formation is of NaHCO3 water type, with the characteristics of low salinity（＜8.0 g/L）, low Cl- concentration, and high HCO3- concentration, which are obvious different with Well WG1 in nearby Wangguantun buried hill. By testing the hydrogen and oxygen compositions of the present formation water, analyzing the lithofacies, homogeneous temperature and paleo-salinity of fluid inclusions, the origin of Permian formation water and its petroleum geological significance are revealed. The results show that: (1) The distribution of hydrogen and oxygen isotope compositions is far from the curve of atmospheric precipitation, indicating that it is weakly influenced by the present atmospheric precipitation. (2) The peak value of homogenization temperature of hydrocarbon inclusions is mainly distributed in the range of 130-150℃, indicating that it is mainly formed in the late stage of reservoir formation. (3) The initial values of paleo-salinity of formation water in some inclusions are less than 5，, and there is a significant decrease in the accumulation period, indicating that the formation water has undergone a desalination process. (4) At the end of the Late Cretaceous, formation water desalination was mainly influenced by infiltration of atmospheric water. After that, the impact of atmospheric water infiltration gradually weakened due to the continuous deep burying of strata. During the sedimentary period from Shahejie Formation to Minghuazhen Formation, the Carboniferous-Permian coal measures strata were compacted and drained, and the drained low salinity formation water entered the adjacent Permian sandstone reservoir, which led to further desalination of the reservoir formation water. (5) Formation water desalination promotes the formation of secondary pores, improves the physical properties of the reservoir, and forms carbonate cement locally, which enhances reservoir heterogeneity. The desalination process of formation water is synchronized with the migration and filling of oil and gas, and the flow direction of formation water indicates the direction of migration and accumulation of oil and gas.