Silicon carbide quantum dots (QDs) were prepared by simple chemical etching method using a mixture of hydrofluoric acid, nitric acid, and analytically pure sulfuric acid as etchants. Ultrasonic cavitation fragmentation was performed on the corrosive mixture, and then it was subjected to high-speed tomographic cutting in a concentration gradient solvent to obtain silicon carbide QDs with excellent optical properties and controllable particle size. The evolution process of microstructure of SiC QDs during corrosion process, the microstructure and emission spectra of SiC QDs were detected and analyzed, and then correlation mechanism at quantum dots size, spectrum, and color was established by emission spectra as a link. The results show that under the conditions of a=1 000 hypergravity coefficient and a centrifugation time of 120 min, the average diameter of QDs at 0, 30, and 60 mm displacement from the liquid surface is about 2, 5, and 7 nm. Under single wavelength excitation, as the diameter of SiC QDs changes from 2→5→7 nm, the relative intensity peak of photoluminescence shows a red shift from 417→435→445 nm, and the luminescence color also show a corresponding change pattern of blue green→green→yellow green; further research had found that the full width at half maximum of the emission spectra of QDs of three sizes show an increase of 81→97→106 nm with increasing liquid depth. Preliminary analysis suggests that it was due to the higher uniformity of particle size distribution of quantum dots near the upper liquid surface compared to those far away from the upper liquid surface after high-speed centrifugal chromatography cutting.