With the strengthening of environmental awareness and regulations, waterborne polyurethane (WPU), as an environmentally friendly water-based resin, has been widely applied and studied. Currently, one of the main issues with WPU products in the adhesive field is the solid content. Excessive water content in the product leads to problems in drying, production efficiency, and adhesive performance. This paper provides a review of research methods for preparing high solids low viscosity WPU in recent years, including optimizing the phase inversion process, increasing space utilization, reducing hydration layer, combining internal and external emulsification methods, and hyperbranched structures. The review summarizes the impact of different factors on the phase inversion process and explains how to optimize this process through changes in techniques and equipment. Suggestions are presented for addressing factors that restrict solid content, such as limitations in emulsion particle packing density, hydration layer thickness, and viscosity. By increasing the solid content, the slow drying and insufficient bonding capacity issues in waterborne polyurethane adhesives can be resolved. This review has practical significance for optimizing the preparation and application of WPU adhesives.