question: Background: Coronavirus Disease 2019 (COVID-19) is a novel infectious disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in Wuhan and has quickly spread across the world. The mortality rate in critically ill patients with COVID-19 is high. This study analyzed clinical and biochemical parameters between mild and severe patients, helping to identify severe or critical patients early. Methods: : In this single center, cross-sectional study, 143 patients were included and divided to mild/moderate and sever/critical groups. Correlation between the disease criticality and clinical features and peripheral blood biochemical markers was analyzed. Cut-off values for critically ill patients were speculated through the ROC curve. Results: ： Significantly, disease severity was associated with age (r = 0.458, P < 0.001) , comorbidities (r = 0.445, P < 0.001) , white cell counts (r = 0.229, P = 0.006) , neutrophil count (r = 0.238, P = 0.004) , lymphocyte count (r = -0.295, P < 0.001) , albumin (r = -0.603, P < 0.001) , high-density lipoprotein cholesterol (r= -0.362, P < 0.001) , serum potassium (r = -0.237, P = 0.004) , plasma glucose (r = 0.383, P < 0.001) , total bilirubin (r = 0.340, P < 0.001) , serum amyloid A (r = 0.58, P < 0.001) , procalcitonin (r = 0.345, P < 0.001) , C-reactive protein ( r = 0.477, P < 0.001) , lactate dehydrogenase (r = 0.548, P < 0.001) , aspartate aminotransferase (r = 0.342, P < 0.001) , alanine aminotransferase (r = 0.264, P = 0.001) , erythrocyte sedimentation rate (r = 0.284, P = 0.001) and D-dimer (r = 0.477, P ＜ 0.001) . Conclusion: With following parameters such as age > 52 years, C-reactive protein > 64.79 mg/L, lactate dehydrogenase > 245 U/L, D-dimer > 0.96 ug/mL, serum amyloid A > 100.02 mg/L, or albumin ＜ 36 g/L, the progress of COVID-19 to critical stage should be closely observed and possibly prevented. Lymphocyte count, serum potassium and procalcitonin may also be a prognostic indicator.