Polyploidization is a key driving force that plays a vital role in the evolution of higher plants. Autopolyploid plants often demonstrate altered physiology phenomena due to the different genome composition and gene expression patterns. For example, autopolyploid plants are more resistant to stresses than their homologous diploid ancestors. Soil salinity and secondary salinization are two vital factors affecting crop production which severely limit the sustainable development of agriculture in China. Polyploid plants are important germplasm resources in crop genetic improvement due to their higher salt tolerance. Revealing the mechanism of salt tolerance in homologous plants will provide a foundation for breeding new plants with improved salt resistance. In this review, we describe the existing and ongoing characterization of the mechanism of salt tolerance in autopolyploid plants, including the salt tolerance evolution, physiology, biochemistry, cell structure and molecular level researches. Finally, we also discuss the prospects in this field by using polyploid watermelon as an example, which will be helpful in polyploid research and plant breeding.