The shortage of freshwater resources is a major global challenge. Solar-powered seawater desalination technology utilizes the naturally abundant resources of solar power and seawater as power and treatment sources, respectively. It is a sustainable solution to the problem of freshwater shortage and can minimize the consumption of fossil fuels and reduce carbon footprint. However, efficient and low-cost solar interfacial evaporators are still in short supply. In this study, we obtained photothermal fibers with optimal photothermal effects and efficient water transfer abilities through the hydrophilic modification of polyacrylonitrile fibers and the deposition of polypyrrole. Taking advantage of its flexible processing properties, an economical and efficient interfacial evaporator was prepared by wrapping fibers onto low-cost insulation material-expandable polystyrene.The heat and mass transfer law of interfacial evaporators with different numbers of water transfer channels was studied. This study provides a theoretical basis and new insights into the development of solar interfacial evaporators.