The scyphozoan Aurelia aurita (Linnaeus) is a cosmopolitan species,having been reported from a variety of coastal and shelf sea environments around the world.The blooms of Aurelia sp.have caused ecological disasters in recent years.In order to discover the key process of the sexual reproduction biology of Aurelia sp.,the spermiation inductive factors,as well as the process of fertilization and embryonic development,were observed according to experimental ecology and microscopy in this study.The results were as follows:the long photoperiod(14L:10D),starvation and damage could effectively induce the sexual matured Aurelia sp.spermiation.The detail information was shown in Tab.1,Tab.2 and Tab.3 respectively.Female Aurelia sp.medusae captured sperm filament that the male released into food bag of somatic edge in which the sperm filament became sperm gobbet by tentacle.The sperm gobbets were transported into oral arm groove by oral arm,then they went through gastric-oral arm groove and gastric reproduction groove successively,and arrived at female gonad to fertilize finally.The fertilized eggs of Aurelia sp.were round and the diameter was about 150 μm.According to the appearance and characteristics of the embryo,embryonic development was divided into 6 consecutive stages:cleavage stage,blastulation stage,blastula stage,gastrulation stage,gastrula stage,planula stage and four tentacles scyphistoma.In (22±1) ℃ sea water,the embryo developed into planula at about 29 h 20 min and grew into four tentacles scyphistoma at about 73 h 20 min.Aurelia sp.Underwent internal fertilization and embryo developed in vivo.The reproductive pattern could improve the survival rate of offspring,which may be the reason why Aurelia sp.existed extensively.