Abstract: Objective To explore the effect of free posture to exert and deliver in the second stage of labor. Methods A total of 320 low risk primiparas were randomly divided into observation group and control group with 160 primiparas in each group.The observation group took free posture in the second stage of labor,while control group took supine lithotomy position.The effect was measured by comparing the time of the second stage,delivery mode,neonatal asphyxia,postpartum hemorrhage,perineal lacerations,lateral episiotomy and pain index. Results The spontaneous delivery rate of the observation group was 85%(136/160),significantly higher than 70.6%(113/160) of the control group,(χ²=3.22,P<0.05).In the observation group,the integrity rate of perineum was 15.0%(24/160),significantly higher than 4.3%(7/160) in the control group(χ²=10.56,P<0.05).The lateral episiotomy rate in the observation group 3.1%(5/160)was significantly lower than 20.0%(33/160) in the control group(χ²=17.14,P<0.05).There was no severe pain in the observation group,while in control group there were 38(24%)severe pain cases(χ²=38.03,P<0.05).The time of the second stage in the observation group (38.9±18.6) min was significantly shorter than (58.6±23.7) min in the control group(t=6.54,P<0.05).The percentage of postpartum hemorrhage was not significantly different(χ²=0.11,P>0.05) between the two groups.The percentage of neonatal asphyxia was not significantly different(χ²=0.389,P>0.05) between two groups. Conclusion The free posture in the second stage of labor could increase rate of vaginal delivery,reduce rate of perineal lacerations and lateral episiotomy,relieve maternal pain and reduce time of the second stage.Besides,free posture in the second stage of labor did not increase neonatal asphyxia and postpartum hemorrhage.Therefore,it is worth recommending in clinical applications.