The invention provides a cubic boron nitride monocrystal purification method. The method comprises the steps of firstly, preparing ammonium base salts according to the ratio, wherein water, ammonium bifluoride and an ammonium salt addition agent are taken on the basis that the ratio of the water to the ammonium bifluoride to the ammonium salt addition agent is 1:6-10:0.5-3; secondly, performing reactive separation, wherein the obtained ammonium base salt mixing solution is poured into a reaction kettle, and the mixing solution is added into a cubic boron nitride concentrate obtained through a conventional tabling method on the basis that the ratio of the cubic boron nitride concentrate to the mixing solution is 1:1-2, and then heating is performed for a reaction for 60-120 min at the temperature being 130-150 DEG C; thirdly, performing filtering and cleaning, wherein tap water is used for filtering out feed liquid obtained from the reaction in the second step, and the obtained cubic boron nitride obtained after filtering is performed is cleaned thoroughly through the clean water and then placed into a drying oven to be dried. According to the cubic boron nitride monocrystal purification method, the production technology is simplified, the cost is lowered, the industrial continuous operation is facilitated, emission is controllable, no harm is caused to the human body, and it is ensured that boron nitride and other impurities in the cubic boron nitride monocrystals are removed.