Abstract: OBJECTIVE To investigate the risk factors associated with the progress of COVID-19. METHODS Literatures search was performed to identify eligible studies published prior to March 2, 2020. Meta analysis were performed with Stata 12.0. Seven case-control studies were eligible involving 1 541 patients with COVID-19, including 139 critically ill patients and 1 402 non-critically ill patients. The clinical characteristics, laboratory findings, CT findings on admission and complications were compared between the two groups. RESULTS ①The mean age of critically ill patients was significantly higher than that of non-critically ill(62.13±14.08) vs (46.08±15.57), WMD=14.57, 95%CI 13.28-15.86, P<0.001. ②The patients with underlying comorbidities were more likely to progress to critically ill (62.6% vs 23.0%, OR=4.90, 95%CI 3.31-7.26, P<0.001), especially with chronic obstructive pulmonary disease (OR=14.71, 95%CI 4.84-44.68, P<0.001). Fever was the most common symptom on admission (86.5%, 1 297/1 500). However, the temperature was not related to the severity of the disease. ③The patients with dyspnea and bilateral involvement of CT scan on admission were associated with an increased risk of critically ill(OR=6.83, 95%CI 4.58-10.16, P<0.001; OR=1.80, 95%CI 1.09-2.96, P=0.021). ④About 51.7% and 57.1% of critically ill patients were complicated with acute respiratory distress syndrome and cardiac abnormalities. However, the incidence of shock and renal injury was relatively low, only 19.8% and 8.6%. This suggested that it was very important for COVID-19 patients to perform cardiac, pulmonary and renal function tests during the clinical diagnosis and treatment. ⑤The lactate dehydrogenase(LDH) level of critically ill patients was significantly higher than that of non-critically ill patients(434.84±208.68) vs (235.45±75.75), WMD=141.79, 95%CI 112.44-171.15, P<0.001, and patients with elevated LDH were more likely to progress to critically ill (72.5% vs 37.9%, OR=3.94, 95%CI 2.25-6.93, P<0.001), suggesting that the LDH level was associated with the severity of the disease. CONCLUSION Old age, underlying comorbidities, dyspnea and bilateral pneumonia on admission may be potential risk factors for critically ill patients with COVID-19. LDH can be used as a monitoring index for disease progression.