The existences of agencies and remainders that have not react with diamond in polycrystalline diamond （for short PCD） influence its performances. The problem can be solved very well through sintering nanodiamond with no or a few agents. But nanodiamond easily absorbs impurities, which prevent the dangling bonds of its surfaces from bonding freely and quick nanodiamond graphitization during its sintered process. Those prevent nanodiamond from sintering. Thus, how to remove the impurities of its surfaces becomes the keystone of this paper.In this paper, we introduced methods of treating nanodiamond using potassium permanganate solution, in vacuum, in hydrogen after being in vacuum and in inter gases circumstances. XRD, TEM, FTIR, DTA and DSC were used to analyze the heat stability and functional groups of untreated and treated nanodiamond.All results showed that its starting oxidation and graphitization temperature was about 550, 1184 and 1381 centigrade in air, in argon and in vacuum circumstance respectively.Using potassium permanganate solution, in air, in vacuum and in inert gases circumstances methods to treat nanodiamond, could remove the functional groups of its surfaces partly. But these methods could introduce more impurities, made it oxidize and graphitize, couldn"t solve second absorption problem. So these methods had some disadvantages respectively. Functional groups could be removed partly by treating it in hydrogen after being in vacuum. Dangling bonds bonded freely after its absorptions desorbed or substituted by hydrogen. As a result the second absorption problem was solved.These results about treating nanodiamond are helpful to the following research on the synthesis of polycrystalline nanodiamond.