Freshwater scarcity has gradually become a serious global water crisis that needs to be solved urgently. Membrane distillation (MD) has been regarded as a promising desalination technology due to its merits compared with other desalination technologies, including high rejection of non-volatile components and superior feed water salinity tolerance. However, the conventional MD faces several challenges, including thermal loss and membrane scaling. Here, we develop a natural products-based Janus sodium alginate/melanin nanoparticles-composited polyvinylidene fluoride membrane (SA-M-PVDF membrane) with outstanding photothermal effect and high hydrophilicity, which can allow the SA-M-PVDF membrane to present excellent photothermal membrane distillation (PMD) performance and scaling-resistance property respectively, thus can solve the hard problems of thermal loss and frequent membrane scaling. Moreover, owing to the biomaterial characters of melanin nanoparticles and SA, the synthesis of SA-M-PVDF membrane circumvents risk of secondary pollution to product water. As expected, the SA-M-PVDF membrane showed excellent PMD performance with 96.5 % solar energy utilization efficiency. The SA-M-PVDF membrane exhibited high scaling-resistance ability and robust structural stability, sustaining over 40 h of continuous PMD operation with high-salinity feed, prospectively providing a facile and environmental approach for sustainably alleviating the freshwater and energy shortage.