To investigate the correlation between serum brain natriuretic peptide (BNP) level of pregnant women with early-onset severe preeclampsia and their cardiac function classification  and left ventricular function. Methods: 55 women with early-onset severe preeclampsia were selected in study group and were divided into group A (women with NYHA I-II cardiac function) and group B (women with NYHA II-IV cardiac function) according to the New York Heart Association (NYHA) cardiac function classification from March 2015 to March 2016. 55 normal pregnant women were selected in the control group during the same period. The serum brain natriuretic peptide (BNP) level, the values of left ventricular end-diastolic diameter (LVIDd), left ventricular end-systolic diameter (LVIDs), right atrial diameter (RVDd), and left ventricular ejection fraction (LVEF) by echocardiographic examination of women in these groups were examined and their differences were observed. The correlation between the serum BNP level and the values of NYHA and LVEF was analyzed. Results: The LVIDs value, and the levels of serum CK, CK-MB, LDH, and NT-ProBNP of women in the study group were significant higher than those of women in the control group, but the LVEF value of women in the study group was significant lower. The LVIDs value, and the levels of serum CK, CK-MB, LDH, and NT-ProBNP of women in group A were significant lower than those of women in the control group, but the LVEF value of women in group A was significant higher (all P＜0.05). Correlation analysis showed that serum BNP level was negatively correlated with LVEF value (r=-0.561, P=0.000) and was positively correlated with NYHA value (r=0.432, P=0.002). Conclusion: Serum BNP level of pregnant women with early-onset severe preeclampsia is high, and the high BNP level is associated with the cardiac function and left ventricular ejection function decreased.