Preeclampsia (PE) is a disorder that affects approximately 5% to 10% of pregnant women. Timely and accurate identification of PE and assessment of its severity are crucial. Therefore, it is necessary to develop predictive indicators which are easily measured in routine antenatal examinations to enable the early detection of PE and assess its severity. We designed a single-center retrospective study in our daily work to assess whether the serum levels of fibrinogen to albumin ratio (FAR), fibrinogen (Fib), albumin (ALB), prothrombin time, calcium (Ca), activated partial thrombin time, creatinine (Cr), D-dimer(D-D), platelet, white blood cell, neutrophil, and lymphocyte counts could help in assessing PE and evaluating its severity. Our findings showed that the serum levels of FAR, Cr, Fib, and D-D were significantly higher in the severe preeclampsia group (sPE) compared with the control and mild preeclampsia groups, whereas the levels of ALB and Ca were significantly lower in sPE patients. In addition, no differences were found between the control and PE groups in terms of prothrombin time, activated partial thrombin time, platelet, white blood cell, neutrophils, and lymphocytes counts. Furthermore, FAR is a novel and better indicator for evaluating the severity of PE, which has not been reported before. And it is an independent risk factor for the development of sPE. In conclusion, the serum levels of FAR, Cr, D-D and Fib were positively correlated with PE, whereas ALB and Ca were negatively correlated with PE severity, which might be valuable in evaluating the severity of PE. FAR proved to be a feasible diagnostic marker for sPE with sensitivity and specificity comparable to those of ALB and Fib.