Abstract: Petroleum traps in syncline can de divided into four types: (l)syncli-nal bedded traps; (2) synclinal locally sealed traps; (3) synclinal subtle traps;(4)synclinal flank-sheltered traps. At present,lens,lithologic pinch-out, fissured and subtle petroleum traps have been found in the synclines of Songliao, Bohai Gulf and Sichuan Basin. It is predicted that new types of petroleum trap occupying a large area will be found in the syncline.