Abstract: Different types of discontinuities in deep rocks have different effects on the stabilities and water-sealed conditions of underground water-sealed oil storage caverns. So it is very important to identify different types of discontinuities in deep rocks and study the development of the discontinuities. This paper uses the results of drillhole image technique to study the issue in association with the project of underground water sealed oil storage caverns in Huangdao. The drillhole image characteristics of four types of discontinuity are analyzed from the aspects of the shape, width, color and interlace characteristics of the curve as well as the rock characteristics near the curve. The drillhole image in the drillhole ZK8 from 120 m above the sea level to 60m below the sea level is taken to identify different types of discontinuities in rocks and study the development of the discontinuities. Results obtained indicate follows: (1) The discontinuity characteristic of one classification is different from the others. So the development characteristics of the deep-discontinuities can be studied by different classifications according to the drillhole images. (2) The amount of tectonic joints and metamorphic differentiation discontinuities both becomes lower along the direction of depth. The metamorphic differentiation discontinuities only develop above the elevation of 30 m. Dike intrusion joints develop in local areas. Thus their influences to the stabilities of the caverns depend on their positions developed. Therefore, the development characteristics of discontinuities in deep rocks should be paid attention, which can be used for engineering construction.