In this paper, the chromosome number of F9-F11 hybridis of Red crucian (Carassius auratus) x common carp(Cryprinus carpio) was examined by means of kidney cell-PHA culture. The results showed that F9-F11 allotetraploids possessed 200 chromosomes, with the karyotype formula 44 m + 68 sm + 44 st + 44 t, which were the same as the data indicated in F3-F8 allotetraploids. Both female and male of F9-F11 allotetraploids had the normal ovaries and testes that were able to produce the normal dipoid ova and sperm. In nature conditions, without the injection of the extraneous hormone, the females and males of F9-F11 allotetraploids mated each other to produce new generation of tetraploids. With the stable genetic tetraploidy and the fertility in the nature environments, this allotetraploid population presented the key factors to form a new species with 200 chromosomes.