Some methods of capillary gas chromatography, such as GC, GC-MS, GC-FT-IR, are used to analyze the products of thymine irradiated by ¹⁸O⁸⁺ ion beam in N²O saturated aqueous solution. From the results of GC-MS the molecular weight of products can be determined, and from the results of GC-FT-IR some molecular structure information of products can be obtained. By this way the products, 5,6-Dihydrothymine, 5-Hydroxyl-5-Methylhydantoin, 5-Hydroxyl-6-Hydrothymine, 5-Hydro-6-Hydroxylthymine, 5-Hydroxymethyluracil, Trans-Thymine glycol, Cis-Thymine glycol and dimers are determined without separation of them from samples. Though these products are as same as those products of thymine irradiated by γ rays in N₂O saturated aqueous solution, the mechanism of thymine irradiated by heavy ion beam in aqueous solution is different from that by γ rays. The main products of thymine irradiated by ¹⁸O⁸⁺ ion beam in N₂O saturated aqueous solution are hydroxyl adducts at 5-6 band of thymine, while the main products of thymine irradiated by γ ray in N₂O saturated aqueous solution are dimers of thymine.