The invention relates to a leak-blocking adhesive and a preparation method thereof. The adhesive consists of the following components in part by weight: 15 to 25 parts of synthetic resin, 15 to 30 parts of lubricating grease, 10 to 15 parts of foaming agent, 20 to 35 parts of fibrous filler, 30 to 50 parts of heat-resistant filler and 5 to 10 parts of coloring agent; the synthetic resin, the foaming agent, the heat-resistant filler and the coloring agent are uniformly dispersed and then are added with the lubricating grease and the fibrous filler, the uniformly mixed materials are added into an extruder and are extruded to form a stick shape, and after being cooled to the room temperature, the stick-shaped adhesive is cut. Compared with the prior art, the leak-blocking adhesive can tolerate most of chemical media, is highly universal, can be automatically filled into a neighboring gap when being heated, enhances the leak-blocking effect, prevents the phenomena of adhesive leakage and adhesive spouting, has excellent flowing property before being solidified, is convenient and easy to operate, and has a wide resisted temperature range.