The seismic response characteristics of oil layer and water layer are close, and conventional fluid prediction methods cannot get satisfactory result for oil layer prediction. Through integrated study of well logging, geology and geophysics, and statistical analysis of theoretical model and field data, the seismic response characteristic of oil-rich reservoir was analyzed from the point of the relative variations of amplitude and sweetness, and its regularity was summarized quantitatively. The results show that when the thickness of oil layer is small, the relative variations of amplitude and sweetness are small too, and they have no obvious relationship with the thickness of oil layer.