The invention discloses safe, environmentally-friendly, efficient and harmless slow release insecticidal granules and a preparation method thereof. The safe, environmentally-friendly, efficient and harmless slow release insecticidal granules include, by weight parts, 8-10 parts of compound plant alkaloid, 20-30 parts of insecticidal plant extract, 40-50 parts of slow release filling, 4-6 parts ofpenetrant, 3-5 parts of adhesion aid and 4-6 parts of modified biochar. The safe, environmentally-friendly, efficient and harmless slow release insecticidal granules have a good slow release effect, long effective time, excellent insecticidal and insect repellent effects, can delay the generation of pesticide resistance of pests, are stable in quality and have stability in storage. Active ingredients and degradation products of the slow release insecticidal granules have very good compatibility with the environment. The slow release insecticidal granules have no residue, are free of pollution,safe, environmentally friendly, have no phytotoxicity to crops, and are safe for humans and animals. At the same time, the preparation method has low production cost, is simple in process and has high practical value and good application prospect.