The work aims to review the preparation methods and properties of two-dimensional nanosheet/polymer composites with high barrier properties to provide a reliable basis and literature support for the preparation of such composites. Based on the modification methods and application scenarios of different two-dimensional nanomaterials, the composite methods of two-dimensional nanomaterials and polymers were summarized, and their barrier effects were compared and analyzed to find high-barrier two-dimensional nanosheet/polymer composites that met application requirements. Different types of two-dimensional nanomaterials had different physical properties and modification methods. There were also various composite methods for two-dimensional nanosheets and polymers. The formed composites had significant differences in barrier properties and barrier mechanisms. In conclusion, the barrier properties of two-dimensional nanomaterial/polymer composites are determined by multiple aspects, including the morphology and structure of two-dimensional nanomaterials, dispersion characteristics, and compatibility with the polymer matrix. This provides ideas and guiding methods for the design of polymer composites with high barrier properties.