A novel method to fast characterize cell differentiation of Haematococcus pluvialis SCCAP k-0084 by cell osmotic sensitivity of motile cells and non-motile cells on Triton X-100 was proposed and then cell propagation and differentiation of H. pluvialis in two fresh medium BG11 and BBM were investigated. It was found that BBM medium kept a high percentage of motile cells in the first 8 d cultivation. In contrast, the released motile cells gradually transformed to non-motile cells. The cell proliferation in BBM medium is contributed by both mitosis and the formation of sporangium of motile cells. It is proved that such differences of cell propagation and differentiation are produced by that the low phosphorus concentration in BG11, indicating the importance of appropriate phosphorus concentration in medium to maintain the continuous division of motile cells.