The inner tube assembly often falls into the hole due to breaking off of the core drilling string. This paper analyzes the existing fishing difficulties and the measures to be taken, and describes the design of two sets of fishing tool in view of the actual situation of two different drilling holes. The inner tube assembly which was completely exposed in the hole was successfully fished out of the hole, avoiding abandonment of the borehole, saving drilling time, and reducing economic loss. Practice has proven that these tools are effective.