Abstract: In order to investigate the changes of chemical compositions in tobacco during primary processing, the total alkaloid, free nicotine and aroma constituents including acidic, basic and neutral constituents in cut tobacco of two cigarette brands were extracted with simultaneous distillation and extraction equipment and analyzed by GC and GC/MS before and after HXD.The results indicated that, after HXD, free nicotine and total alkaloid decreased nearly 30% and 16%, respectively, ketones and the(total) amount of basic aroma constituents tended to decrease, while alcohols, especially acidic aroma components increased obviously, the contents of acidic aroma components in the two brands raised by 18% and 31%, respectively.