Objective To analyze the changes of plasma P-LAP (placental leucine aminopeptidase) and IL-6 (interleukin-6) levels in spontaneous preterm pregnant women in the third trimester of pregnancy. Methods 126 cases of spontaneous preterm pregnant women from west China Second Hospital，Sichuan University were selected as spontaneous preterm group and at the same time selection in the hospital 126 cases of healthy full term pregnant women as control group.The plasma P - LAP and IL - 6 level were detected and analyzed. Results Compared with the control group，the levels of plasma P-LAP and IL-6 were lower and higher in the spontaneous preterm group at 28-32 weeks and 33-37 weeks，the differences were statistically significant (P<0.01). The levels of P-LAP and IL-6 in the spontaneous preterm group at 33-37 weeks and 28-32 weeks were statistically significant (P<0.01). Compared with the group without SC spontaneous preterm delivery at 28-32 weeks and 33-37 weeks，the P-LAP level was lower and the IL-6 level was higher in the group with SC spontaneous preterm delivery，and the difference was statistically significant (P<0.01). The results of Pearson correlation test showed that plasma P-LAP was negatively correlated with IL-6 (r=-0.312，P<0.01) in spontaneous preterm delivery women. After analysis，98 cases were found abnormal by P-LAP test，97 cases were found abnormal by IL-6 test，122 cases were found abnormal by combined test，and more people were found abnormal by combined test. The sensitivity，specificity and accuracy of the combined test were significantly higher than those of the single test，and the difference was statistically significant (P<0.01). Conclusion To strengthen the joint detection of P-LAP and IL-6 level in spontaneous preterm delivery of pregnant women in the late trimester has a positive effect on the prediction of preterm delivery，and is helpful for clinicians to timely implement targeted program intervention according to the test results，ensure the pregnant women to deliver at term，and improve the quality of life of mothers and infants.