The invention provides quantum dots and a preparation method thereof. The preparation method comprises the following steps: (1) mixing a body material, a grinding aid material and a ball milling ball,and carrying out ball milling to obtain a crude product; and (2) mixing the crude product obtained in the step (1) with a solvent to obtain a mixed solution, and carrying out ultrasonic treatment onthe mixed solution to obtain the quantum dots. The preparation method is a top-down preparation strategy, a macro-scale body material is used as a raw material, the body material is effectively crushed through the synergistic combination of two physical methods of ball milling and ultrasonic treatment, and finally, the nano-scale quantum dots with uniform particle size are obtained. The preparation method has the advantages of being efficient, environmentally friendly, easy to operate, low in cost and the like, is suitable for large-scale production and has good application prospects, the prepared quantum dots are high in purity, good in dispersity, high in yield, uniform in particle size and controllable in size, and the preparation method has important guiding significance in achieving industrial application and accelerating the industrial process of the quantum dots.