The invention provides a preparation method for a long-acting slow-release chlorine-based nitrogen and potassium-containing compound fertilizer. The compound fertilizer belongs to mixed fertilizers containing substances affecting nitrification of ammonium-containing compounds or urea in soil, and is characterized by being prepared by: first preparing chlorine-based nitrogen and potassium-containing compound fertilizer granules, and then performing primary coating and a secondary surface powder putting by using a modified zeolite powder to the chlorine-based nitrogen and potassium-containing compound fertilizer granules by using stearic acid; wherein: the chlorine-based nitrogen and potassium-containing compound fertilizer is prepared from the following raw materials, by weight: 30-60 parts of urea, 10-20 parts of ammonium chloride, 22-53 parts of potassium chloride, 7-11 parts of granulating aids, and an appropriate amount of water. Provided is a preparation method by using which a long-acting slow-release chlorine-based nitrogen and potassium-containing compound fertilizer having good slow-release effect and high fertilizer utilization rate can be produced, wherein the elemental chlorine in the compound fertilizer can play a full role in the growth of crops, the process is simple, the production cost is low, and coating materials are easy to be degraded in the soil by microbes, which is beneficial to soil, air and water environmental protection. The long-acting slow-release chlorine-based nitrogen and potassium-containing compound fertilizer has a good sustained-release effect, and high fertilizer utilization rate, suitable for applying to various crops.