The water property judgment of gas field produced water is particularly important for gas field development. If there is no water property determination law, the development and production of gas field and the evaluation process of rolling exploration and development will be seriously restricted. Due to the difference of favorable reservoir layers and formation water properties in each area, and the influence of drilling and other engineering fluids, the determination law of produced water property be-comes more complex It can adopt the unified water property judgment law. In order to deepen the understanding of produced water in gas field, it is necessary to study the water property characteristics and determine the water property in the early stage of gas field development. Therefore, this paper proposes a three-step process to deter-mine the water quality of gas field produced water: first, according to the results of logging interpretation and sampling analysis of produced water, initially form the boundary index for judging the water property; secondly, analyze the physical, chemical and chemical characteristics of different water properties Finally, the rule of gas field water property is formed. This paper also reveals the variation law of chemical characteristics, chemical characteristic coefficient and physical characteristics of different water properties. The salinity, chloride ion modification coefficient (Cl_-Na +)/Mg2 + and Cl_/Mg2 + are in the order of formation water > Engineering Flu-id > condensate water; the content of trace elements is shown as formation water >  > Engineering Fluid > > condensate water; the characteristics of major elements in formation water of each gas field are very similar; anion Cl_ and salinity are similar The relationship between other ions and mineralization is not obvious.