The work is to study the mechanism of toxic effects on reproductive system and apoptosis of Chinese hamster ovary (CHO) cells induced by X-rays. CHO cell was exposed to X-rays 2 to 20Gy, Apoptosis and morphological changes of the cells were observed by fluorescent microscopy and flow cytometry analyzer with double staining with Annexin V/ PI. The apoptosis could be observed at 24, 48 and 72h after the exposure, but it was more obvious 48 and 72 h after the exposure. Rate of the apoptosis increased along with radiation dose were elevated. Some morphologyical changes, such as irregular agglomerate of chromatins, pycnosis and periphery distribution of nuclei, crescent-moon-like cell, small apoptosis body, were observed. Radiation results DNA damage in the CHO cells, and the demage cannot be repaired, hence the induced cell apoptosis.