The invention discloses the application of 8-alkyl berberine salt to the preparation of a medicine for preventing and treating lung cancer. The 8-alkyl berberine salt adopts a molecular structural formula as shown in the specification, wherein X is F-, Cl-, Br- or I-, R1 is CnH2n+1, and n is 12-22. The compound 8-alkyl berberine salt has a relatively good anti-lung cancer effect, and especially when the carbon number of an alkyl chain is 16-22, the anti-lung cancer effect thereof is obviously superior to that of berberine salt; the 8-alkyl berberine salt can be applied to the preparation of the medicine for preventing and treating the lung cancer.