Abstract: PML-RARA transgenic （Tg） mice developed acute promyelocytic leukemia （APL） with APL features which provided us with a powerful model to further our study on the mechanism of APL. Tg mice were observed and peripheral blood（PB） analysis was done at scheduled time. Tg mice of different ages were picked up and sacrificed. Phenotypic analysis showed that the course of APL development could be divided mainly into three stages：pre-leukemic stage，early leukemia stage and advanced leukemia stage. Phenotypic features which is specific for each stage could be observed. Thus,screening of Tg mice by using phenotypic analysis （cytologic analysis of PB and bone marrow（BM）,histo-pathology of BM）make it possible for us to pick up the Tg mice at those different stages which is crucial for the study of genetic changes during the development of APL.