Abstract: To study the placental and fetal heart function,cardiopulmonary bypass was established in fetal lambs and the different methods of cannulation were applied.The results showed that the direct pulmonary artery cannulating was more reliable than pulmonary artery cannula ting through right ventricular outflow tract.Besides,the warm-ing of the fetal lamb，avoiding of uterine contraction，umbilical cord twist and bleeding during operation should be also emphasized.