Due to the effect of chromosome doubling, the DNA genetic structures of autotetraploid vary from its original diploid, and thus autotetraploid phenotype changes correspondingly. Compared with original diploid, the phenotype changes of autotetraploid were as follows. The part of its male and female gametes was of abortion. Its pollen (diplo-haplont) was significantly bigger. The number of egg cells or synergids or antipodal cells in its embryo sacs increases or reduces. While self-crossing procreation of it, pollen tubes and the fertilization processes of polar nucleus and the fertilized cells development were partly abnormal. Its reproductive capacity (or seed setting rate) dropped to some extents, which can be gradually improved with generations. For some plant species, it has a better cross-compatibility in distant hybridizations.