This paper explored the effect of prenatal maternal stress on antenatal depressive symptom and the mediating effect of subjective well-being. By using the convenience sampling method, pregnant women who were examined in the obstetrics outpatient department of a tertiary general hospital in Nantong were prepared for the research. The general demographic characteristics of the study subjects were investigated by questionnaires. The psychological state of pregnant women was investigated through the Pregnancy Stress Rating Scale(PSRS), Edinburgh Postpartum Depression Scale(EPDS) and Subjective Well-Being Scale for Chinese Citizen（SWBS-CC20）. Data analysis was performed using the statistical software SPSS 27.0, and mediation effect analysis was performed using the SPSS macro program PROCESS. The results showed that among 653 pregnant women, the incidence of depressive symptoms was 34.0%, and the incidence of moderate to severe prenatal depressive symptom was 9.2%. The relationship between pregnancy stress, subjective well-being, and prenatal depressive symptom showed that the higher score of the stress during pregnancy, the higher risk of prenatal depressive symptom (β=0.262, P<0.001). The lower score of the stress during pregnancy, the higher risk of the subjective well-being (β=-0.284, P<0.001) and the higher level of subjective well-being was associated with a lower risk of prenatal depressive symptom (β=-0.246, P<0.001). Subjective well-being played an incompletely intermediary role in the relationship between prenatal maternal stress and antenatal depressive symptom, with the mediating effect accounted for 26.61% of the total effect. Pregnancy stress can significantly predict prenatal depressive symptom. The subjective well-being played a partial mediating role between pregnancy stress and prenatal depressive symptom. This study suggest that we should pay attention to reduce the stress during pregnancy and continuously improve subjective well-being, so as to reduce the occurrence of antenatal depressive symptom.