Objective To observe the effect of dietary anti-inflammatory index (DII) in the second trimester on the levels of serum inflammatory markers and the pregnancy outcomes in primiparas during pregnancy. Methods From Jul. 2015 to Jul. 2016, a total of 212 primiparas in our hospital were taken as the clinical objects, which were divided into anti-inflammatory proneness group (DII<-5.10), middle group (-5.10≤DII≤-2.55) and proinflammatory proneness group (DII>-2.55). The levels of serum matrix metalloproteinase-3 (MMP-3), tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in the fasting state of pregnant women were tested, and the premature birth rates in the two groups were compared. Results The levels of MMP-3, TNF-α and IL-6 in the proinflammatory proneness group were obviously higher than those in the anti-inflammatory proneness group and middle group(P<0.05). The premature birth rate in the proinflammatory proneness group was obviously higher than those in the anti-inflammatory proneness group and middle group(P<0.05). Conclusion DII index can be used to evaluate the dietary quality and the level of serum inflammatory factors in the second trimester of pregnancy, and premature birth can be effectively prevented by adjusting dietary structure.