Extracted lignan from flaxseed meal by reflux method. The crude extract was preliminary purified by D101 macroporous adsorption resins which was followed by semi-preparation HPLC separation. The semi-preparative HPLC conditions were as follows: column was Megres C₁₈(30 mm×250 mm，10 μm), mobile phase was a mixture of acetonitrile(A)-0.1% phosphoric acid water solution(B), gradient elution,flow rate was 35 mL/min, wavelength was 280 nm, column temperature was 30 ℃ and injection volume was 2 mL. In the conditions, 98% purity flax lignans were obtained. Investigated the protecting activity of lignan against DNA damage that caused by UV photolysis and H₂O₂ treatment, it reveals that flax lignans has a significant effect on the protection of DNA oxidative damage while the concentration is 0.07~0.40 μg/μL.