This study aimed to determine the following: whether Sirt1 and serum vitamin D decreased with physiological aging, promoting senescence‐associated pulmonary fibrosis by activating TGF‐β1/IL‐11/MEK/ERK signaling, whether Sirt1 overexpression prevented TGF‐β1/IL‐11/MEK/ERK signaling‐mediated senescence‐associated pulmonary fibrosis in vitamin D‐deficient (Cyp27b1−/−) mice, and whether Sirt1 downregulated IL‐11 expression transcribed by TGF‐β1/Smad2 signaling through deacetylating histone at the IL‐11 promoter in pulmonary fibroblasts. The gene discussed is SMAD2; the disease is pulmonary fibrosis.