Abstract: Seismic bright spot identification method in oil and gas exploration in recent years have been widely used.According to the basic principle of physical modeling rock,through to the four of forward modeling analysis,discusses different thickness of gas sandstone and surrounding rock(mudstone) amplitude characteristic;Based on the actual well as an example,through its longitudinal wave impedance contrast,analyzes the characteristics of bright spot reasons for difference;Northern south China sea in the deep water area main oil bearing formation L sag,within conventional profile in the bright spot of that can be used as an important basis for the reservoir prediction.