Abstract: Visualization is effective for true 3-D interpretation of 3-D seismic data volume.This paper introduces the basic principles of visualization on 3-D seismic data volume,and the main steps using ray-casting algorithm,develops the computing formulas to compose visualization image,discusses the physical meaning of opacity curve and its adjusting function to visualization image.The results of real cases showed the geologic body can be directly imaged from original 3-D seismic data volume by this method.The scattered,isolated information can be related together to reveal the geologic phenomenon and regular hidden in data.