目的　构建定点突变的小鼠凝血因子Ⅸ胚胎干(ES)细胞基因打靶载体。方法　在小鼠Ⅸ因子基因第8 外显子中分别引入三个定点突变,构建置换型打靶载体转染胚胎干细胞,经药物筛选后挑取抗性细胞。结果　成功引入点突变并构建置换型打靶载体,转染ES细胞后经药物筛选得到抗性细胞克隆。结论　体外定点突变系统可以对基因进行精细的修饰,为建立更精确地模拟人类疾病的动物模型打下基础。 Objective To construct targeted mutagenesis murine clotting factor Ⅸ embryonic stem (ES) cell gene targeting vector. METHODS: Three site-directed mutagenesis were introduced into exon 8 of mouse factor IX gene respectively, and transplanted embryonic stem cells were constructed by transplanting targeting vector. The resistant cells were picked after drug screening. Results The successful introduction of point mutations and the construction of a transformant targeting vector were performed. ES cell transfected cells were screened by drug selection. Conclusion In vitro site-directed mutagenesis system can finely modify the gene and lay the foundation for the establishment of an animal model that more accurately simulates human diseases.