The invention discloses a preparation method of pure silicon beta molecular sieve nanocrystals. The method comprises the following steps: drying 4.21-15 g of a solution with 35% by mass of tetraethylammonium hydroxide at a temperature of 40-90 DEG C for 30-720 min, and uniformly mixing the dried material and 0.8-5 g of white carbon black to obtain a mixture; performing crystallization treatment onthe mixture under steam-assisted conditions to obtain a crystalline product; and cooling the crystalline product, performing washing, performing drying and performing calcination treatment to obtainthe pure silicon beta molecular sieve nanocrystals with high crystallinity. According to the method provided by the invention, a templating agent and water used in the synthetic process are less, andtherefore the method provided by the invention has the advantages of low costs, small environmental pollution, and favorable industrial production.