The heat treatment of ruby belongs to the optimization treatment,and borax is commonly used as the flux. In the market,heat-treated rubies are sold naturally and have a high value,but the amount of borax in the crack will affect the price. Therefore,in this paper,the borax in this kind of ruby was quantitatively studied,and NanoVoxel-4000X X-ray computed tomography was used to scan and analyze the sample,and 2D images of borax filling in fractures were obtained. The grayscale values of light and shade were used to characterize the different densities of the material in the crack,and different colors characterized the 3D images of the borax filling distribution. By comparing the color scale of thickness,it can be seen that the overall content of borax is small. At the same time,the histogram of the borax thickness distribution of samples shows that the thickness of borax in all fractures is less than 130 μm,and the thickness-to-volume ratio of all borax is less than 10%,which also indicates that the filling amount is small. Finally,Avizo 9.0 software was used to segment the ruby sample and borax content to obtain the actual volume of the two. Then,the percentage of borax content in the total volume of the ruby could be calculated. The proportion of borax in the sample is 10.69%,which is not only an important index in the quantitative detection of borax in heat-treated rubies but also provides data support for the study of the quantitative classification standard of borax in heat-treated rubies.