The prospecting of the gas and oil reservoir (field) was one of the major tasks of geophysical exploration. The identification and classification of oil and gas unit was the key to the success or failure of the reservoir (field) exploration, also the major tool and ways for improving the efficiency of oil & gas exploration and reducing the risks in exploration. Through the establishment of horizontally layered model, the geophysical response characteristics of gas, oil and water were analyzed, and a gray system theory was used to extract and analyze the characteristics of seismic data structure. Combined with the actual data, the results show that for the existence of gas and oil, there exists obvious structural abnormality in seismic data, by which the oil and gas units can be identified and classified effectively.