Based on the sex determination of Hymenoptera parasitic wasps that unfertilized egg develops into a male while fertilized egg develops into a female, the insemination potential of male Trichogramma ostriniae and its relationship with body size, age and the number of copulations were studied. The results showed that spermary of T. ostriniae had been set before the eclosion and no sperm was produced in the adult stage. A male adult could inseminate 8-23 females during its lifetime, and approximately breed 346.15 female progenies. Males exhausted their sperms or seminal fluid in 24 hours after emergence when provided with unlimited virgin females. Though male adults would continue to copulate with females afterwards, no female offspring had been observed. The insemination potential of a male T. ostriniae was closely linked with the number of copulations, and sperm quantity gradually decreased as more copulations performed. The male adult could provide more sperms to females in its initial copulation, and approximately fathered 58.85 female progenies. However, with the increase of the number of copulations and consumption of sperms, fewer and fewer sperms could be transmitted to females. A male could father no more than 10 female progenies after 10 copulations. The insemination potential also showed that it was positively related to body size. Bigger males could copulate more and breed more female progenies.