Numerous oil–water mixtures produced through industrial production processes and daily activities pollute the ecological environment and pose risks to human health. The development of materials with high oil–water mixture separation efficiency can promote the recycling of oil and water resources and effectively prevent environmental pollution caused by their direct discharge. Most of the current oil–water separation materials consist of foam, aerogel, and other porous materials. Among these materials, polyurethane exhibits good biodegradability, mechanical properties, large pore volume, low cost, wear resistance, and water resistance in oil–water mixture separation applications. However, pure polyurethane foam is characterized by low adsorption separation efficiency, insufficient recyclability, and high flammability. Therefore, modifying polyurethane to improve the oil–water mixture separation efficiency is vital. In this review, the methods and mechanisms of polyurethane modified materials used for oil–water mixture separation are reviewed, and their future research and application directions are prospected.