The invention provides a preparation method of a carbon-based compound slow-release fertilizer. Raw materials comprise, by weight, 5 to 10 parts of straw biological black carbon, 2 to 5 parts of pyroligneous liquor, 21 to 34 parts of enzyme-free bacteria chicken manure, 10 to 15 parts of bone meal, 18 parts of potassium sulfate, 22 to 24 parts of ammonium biphosphate, 11 to 12 parts of large-granule urea and 2 to 5 parts of water. The preparation method comprises putting the crushed enzyme-free bacteria chicken manure, straw biological black carbon, bone meal, large-granule urea, ammonium biphosphate and potassium sulfate into a ZLC-300 type mixer for mixing and stirring, putting them into a KP-300 type organic fertilizer granulator for granulating after uniformly mixing, adding 2 to 5 parts of the pyroligneous liquor and 2 to 5 parts of water while granulating, naturally cooling the resulting to be lower than 28 DEG C after the granulation, and packaging it, wherein the enzyme-free bacteria chicken manure is disinfected for 2 to 3 hours under 2 Pa in a disinfection pot, dried in a tumble dryer, crushed, and sieved by a 60-mesh sieve, with a water content being less than 11 %.