Some researches have shown that type 2 diabetes mellitus may increase the risk of lung cancer. However, it is still lack of effective evidence on the underlying mechanism. This article reviewed that their epidemiological characteristics, hyperglycemia, insulin resistance and hyperinsulinemia, insulin and insulin-like growth factor, vascular endothelial growth factor, inflammatory cytokines, disorder of hormones regulating function, reduced immune system function, disorder of trace elements and the glucose-lowering therapies in diabetes patients may be associated with an increased incidence of lung cancer. However, more studies are needed to further investigate the mechanism urderlying type 2 diabetes mellitus promoting the incidence of lung cancer.