Objective To investigate the value of CD5 molecule-like protein(CD5L) and partial pressure of CO2 in arterial blood(PaCO2) in predicting the survival of patients with severe asthma and mechanical ventilation.Methods From Jan.2013 to Jan.2016,a total of 38 patients with severe asthma and mechanical ventilation were enrolled.Acute Physiology and Chronic Health EvaluationⅡ(APACHE II)were used to assess the severity.Enzyme linked immunosorbent assay was used to detect serum levels of CD5L at admission and 6 h after treatment.PaCO2 were also detected.Pearson correlation analysis was used to analyze the correlation between APACHEⅡ score and CD5L and PaCO2 levels.Receiver operation characteristic(ROC) curve was used to evaluate the value of CD5L and PaCO2 in predicting the survival of patients.Results APACHEⅡscores of survival patients were significantly higher than dead patients(P<0.05).CD5L level of survival patients after treatment was significantly lower than dead patients,while PaCO2 level was significantly higher(P<0.05).APACHEⅡ score was negatively correlated with serum CD5L level(r=-0.347,P<0.05),while positively correlated with PaCO2 level(r=0.573,P<0.05).ROC curve analysis showed that serum CD5L and PaCO2 were with predictive value for prediction the survival of patients,with sensitivity of 93.33%,specificity of 75.00%,accuracy of 89.47%,positive predictive value of 93.33%,and negative predictive value of 75.00% for CD5L,and those for PaCO2 were 90.00%,87.50%,89.47%,97.42% and 70.00%.Conclusion With the decreasing of CD5L level and increasing of PaCO2 level,severity of disease in patients with severe asthma and mechanical ventilation could be more serious condition,indicating poor prognosis.CD5L and PaCO2 could be with fine predictive value of survival of patients with severe asthma and mechanical ventilation.