Abstract: Objective: To investigate the effect and mechanism of insulin on human lung adenocarcinoma cell strain A549. Methods: Effect of insulin on the metabolism of human lung adenocarcinoma cell strain A549 was analyzed by MTT.Cell cycle was analyzed by flow cytometry（FCM）.Expression of cyclins A and D1 was detected by Western blot. Results: Insulin at the dose of 2.0-32.0mU/mL promoted the proliferation of human lung adenocarcinoma cell strain A549（P＜0.05）.Cell cycle analysis showed that insulin at the dose of 8mU/mL increased the number of human lung adenocarcinoma cells at S phase（P＜0.01）.Western blot displayed that the expression of cyclin D1 was significantly increased,while that of cyclin A remained unchanged after treatment with insulin at the dose of 8mU/mL. Conclusion: Insulin promotes the proliferation of human lung adenocarcinoma cell strain A549,and acts mainly on human lung adenocarcinoma cell strain A549 at S phase.Increased expression of cyclin D1 plays an important role in the proliferation of human lung adenocarcinoma cell strain A549.