Abstract: Polyploidy is an important force of plant evolution. The major cytological mechanisms of polyploid formation are union of unreduced gametes,somatic doubling and polyspermy.And union of unreduced gametes is the most important mechanism.Triploids may play an important role in tetraploids formation.Earlier perception is that polyploids are the evolutionary dead-ends.But an important recent discovery is that most taxonomically recognized polyploid species are of multiple origin,instead of mono-origin.In genomes,most duplicate genes retain original functions,but there are many duplicate genes become silence.Polyploids often show novel phenotypes that are not present in their diploid progenitors or exceed the range of the contributing species,this is because that polyploidy causes changes of gene expression.This article will review and prospect the polyploid research from these aspects: the origin of polyploid, the factors that affect polyploid occur,and the genomes changes of polyploid.