Solar water evaporation technology based on photothermal materials is regarded as one of green and critical technologies for addressing freshwater scarcity. However, practical application of photothermal materials is limited by their high preparation cost, low evaporation efficiency, and poor photothermal conversion. In this study, a facile sponge with excellent photothermal and mechanical properties has been fabricated by mechanical-mixing and chemical-crosslinking of polyethyleneimine modified graphene oxide nanosheets (PEI-GOs), formaldehyde, polyvinyl alcohol (PVA) and sulfuric acid catalyst. The as-prepared PEI-GOs/PVA sponge shows excellent light absorption (95.1 %) under standard sunlight intensity of 1.0 sun (1 kW m^-2) and a wide wavelength range of 200~2500 nm. The achieved high evaporation rate (1.80 kg m^-2 h^-1) is 4.7 times those of pure water (0.38 kg m^-2 h^-1). Moreover, the simulated seawater desalination experiment shows that the sponge has a good long-term stability and an average photothermal conversion efficiency of 88.5 %. The water purified by the sponge exceeds the quality of urban daily water. Therefore, this study offers a new facile route for fabricating a kind of photothermal sponge with good light absorption capacity, and water evaporation properties, which has potential application in seawater desalination.