The blood cytology and histology of formation in Megalobrama amblycephala Yih have been studied. The pulp of spleen,the intertubular tissue of kidney, the sinusoid Of liver and the submucosa of small intestine are main henlato-poietie centers of the fish. The number of blood cells producedly each hematopoietic organs vary monthly. While the parent cells flow from the hematpopietic organs into the peripheral blood vessels complete the process of maturation. The deoelopment of erythrocyte is described in the paper, and the difference between the parent neutro-phils and the matured ones is discussed. But the development of monocytes，lympho-cytes and coarse grannlocytes need to be further studied.