Abstract: This paper deals with the study on the cross fertilization between Carassius auratus red variety (♀) and Cyprinus carpio xiangjianesis (♂).Mature oocytes of C.auratus red variety have a diameter of 680-720 μm.The micropyle is contained by micropylar vestibule (MV) and canal (MC) which has a diameter of 5 μm.While the sperm has a half diameter of MC,through the micropyle only single sperm usully enters the egg,which is known as monospermic egg,C.aurutus red variety and C.carpio xiangjianesis belong different genus,even then the process of their cross fertilization are normal.The appropriate time of insemindtion is at the metaphase of the meiosis.By the 5 min postinsemination,conspicuous spermast is seen in the egg cytoplasm of C.aurutus red variety.By the 15 min postinsemination,the male and female pronuclei are formed.By the 25 min postinsemination,the male and female pronuclei are fused to form the nucleus of the zygote.By the 30 min postinsemination,segmentation begins in the zygote.The 4 pronuclei being fused are found in the section of 1 zygote.Perhaps it comes from bispermism.