Abstract: Taking diploid and autotetrapolid black wax gourd as experimental materials, the effects of pollen morphology and vitality, double fertilization, and embryonic development on the fertility and seed setting rate of diploid and autotetraploid black wax gourd were studied by using optical microscopy and scanning electron microscopy, in order to provide reference for the mechanism of low fertility in self-pollination of autotetraploid black wax gourd.The results showed that the pollen grains of autotetraploid black wax gourd were larger than diploid, there were lots of abnormal structure of pollen grains, and the abnormal rate was 42.43%.The pollen viability of autotetraploid was lower than diploid and the growth speed of pollen tubes was slower than diploid.There was obvious disintegration, degradation or abortion of embryo-sac in autotetraploid black wax gourd, and the abnormal embryo-sac rate was about 40%.The double fertilization process of autotetraploid black wax gourd was delayed by 1 day, and the fertilization rate of autotetraploid was lower than diploid; the dormancy stage of zygote of autotetraploid was longer than diploid, and the embryo development of autotetraploid was later 5 days than diploid.During embryo development, there were higher frequency of embryo development lag, abnormal development of zygote, and lots of endosperm cells with large nuclei, and lots of free nuclei or endosperm cells disintegrated or degenerated at the dormancy stage of zygote and globular embryos stage.