Abstract: Objective To set up the optimized conditions,the amplification of eord blood CDCD+34 cells in vitro were analyzed by comparing the conditions such as different feeder-layers, stimulating-factors or purity/contents of those cells. Methods The cord blood CDCD+34 cells proliferation was analyzed by the methods of MTT, cell counting, and flow eytometer. The amplification and clone-forming ability of cord blood CDCD+34 cells were detected under optimized condition. Resulits The growth rates of cord blood CD+34 cell under optimized conditions(10 times) were significantly higher than that of the control(2.8 times) (P <0.01), and the cloneforming ability of cord blood CDCD+34 cells under optimized conditions(CFU-C 36.67±6.11) were also better than that of the control(CFU-C 16.33±1.53) (P <0.01). Conclusion The cord blood CD+34 cells proliferation can be promoted in the co-cultured system, and the character of the stem cells were kept well in that system.