Objective  To investigate the effectiveness,side effect,outcome of perinatal infants of the expectant treatment in placenta previa with depressant of uterine contraction.Methods  50 wemen with placenta previa of preterm labor were assigned into two groups.30 patients treated with magnesium sulfate and salbutamol were served as study Ⅰ group.20 patients enrolled in the study Ⅱ group,receiving ritodrine.Results  The study Ⅰ group prolonged the gestational period to an average of 27.00 days.The study Ⅱ group prolonged the gestational period to an average of 30.25 days.The difference of two groups had no significance(  P  >0.05).The study Ⅰ group increased the birth weight of newborn to an average of 2?456?g and Apgar score of newborn is 6.75.The study Ⅱ group increased the birth weight of newborn to an average of 3?106?g and Apgar score of newborn is 9.12 (  P  <0.001).Conclusion  Depressant of uterine contraction is highly effective and safe for expectant treatment of placenta previa.The outcome of perinatal infant of the study Ⅱ group is better than that of the study Ⅰ group.