OBJECTIVE: To identify the key biochemical indicators that affect the clinical type and outcomes of COVID-19 patients and explore the application of neutrophil/lymphocyte ratio (NLR) in COVID-19. METHODS: Ninety-three patients with confirmed diagnosis of COVID-19 admitted in Ezhou Central Hospital from February to April in 2020 were analyzed. Among them, 43 patients were selected from Intensive Care Unit (ICU) with the diagnosis of critical type of COVID-19, and 50 cases of common type were selected from the Department of Respiratory Medicine. The baseline data, blood routine test and biochemical indexes of the patients were collected on the first day of admission. NLRs of the patients were calculated, and COX survival analysis according to the NLR 4-category method was performed. The patients' outcomes were analyzed with receiver operating curves (ROCs). The patients were divided into two groups according to NLR cutoff value for comparison of the biochemical indexes. Based on the patients' outcomes, NLR cutoff value classification and clinical classification, multiple binary logistics regression was performed to screen the key variables and explore their significance in COVID-19. RESULTS: The NLR four-category method was not applicable for prognostic evaluation of the patients. The cut-off value of NLR for predict the prognosis of COVID-19 was 11.26, with a sensitivity of 0.903 and a specificity of 0.839; the laboratory indicators of the patients with NLR &lt; 11.26 were similar to those in patients of the common type; the indicators were also similar between patients with NLR>/=11.26 and those with critical type COVID-19. NLR, WBC, NEUT, PCT, DD, BUN, TNI, BNP, and LDH had significant effects on the clinical classification and outcome of the patients (P &lt; 0.05); Cr, Ca, PH, and Lac had greater impact on the outcome of the patients (P &lt; 0.05), while Na, PCO2 had greater impact on the clinical classification of the patients (P &lt; 0.05). CONCLUSIONS: NLR can be used as an important reference for clinical classification, prognostic assessment, and biochemical abnormalities of COVID-19. Patients of critical type more frequently have bacterial infection with more serious inflammatory reactions, severer heart, lung and kidney damages, and much higher levels of DD and LDH than those of the common type. NLR, NEUT, DD, TNI, BNP, LDH, Ca, PCT, PH, and Lac have obvious influence on the prognosis of COVID-19 and should be observed dynamically.