Objective: To study the expression of TNF-α and the function of TNF-α-308 polymorphism in metabolic syndrome patients with asthma. Methods: 112 metabolic syndrome patients without asthma (MS group) treated at our hospital from June 2011 to June 2014 were chose, in the same time, we chose 78 cases with metabolic syndrome complicated with asthma (MA group) and 60 cases of healthy volunteers as control group NC. Biochemical index and pulmonary function of three groups were examined. ELISA was used to detect the protein level of TNF-α. The level of TNF-α mRNA expression in mononuclear cells of peripheral blood was examined by real-time PCR. Fragment length polymorphism PCR analysis method was selected for determination of TNF-α-308 gene polymorphism. Results: The frequency of GA+AA genotype and A allele were significantly increased in MS and asthma patients (P<0.05), GA+AA genotypes and the GG genotype in MA group correlated with higher body mass index, low density lipoprotein, fasting blood glucose, fasting insulin, HOMA-IR, TNF-α, IgE, C alpha in C-reactive protein, endothelin-1 and lower in high density lipoprotein, PEV1 percentage of predicted value, PEV1/FVC and nitric oxide levels. TNF-308 sites (G/A) was positive related with body mass index, diastolic blood pressure, low density lipoprotein, fasting blood glucose, fasting insulin, IgE, C reactive protein, endothelial-1, and negatively correlated with high density lipoprotein, HOMA-IR, PEV1% predicted value, PEV1/FVC and nitric oxide levels (P<0.05). Conclusion: The increase of TNF-α expression and TNF-α-308 gene polymorphism in metabolic syndrome patients may be one of the risk factors inducing asthma.