Abstract: During the continuous casting process of high-Mn high-Al steels, various types of gases such as Ar need to escape through the top of the mold. In which, the behavior of bubbles traversing the liquid slag serves as a restrictive link, closely associated with viscosity and the thickness of liquid slag. In contrast to two-dimensional surface observation, three-dimensional (3D) analysis method can offer a more intuitive, accurate, and comprehensive information. Therefore, this study employs a 3D X-ray microscope (3D-XRM) to obtained spatial distribution and 3D morphological characteristics of residual bubbles in mold flux under different basicity of liquid slag, different temperatures, and different holding times. The results indicate that as basicity of slag increases from 0.52 to 1.03, temperature increases from 1423 to 1573 K, the viscosity of slag decreases, the floating rate of bubbles increases. In addition, when holding time increases from 10 to 30 s, the bubbles floating distance increases, and the volume fraction and average equivalent sphere diameter of the bubbles solidified in the mold flux gradually decreases. In one word, increasing the basicity, temperature, and holding time leading to an increase in the removal rate of bubbles especially for the large. These findings of bubbles escape behavior provide valuable insights into optimizing low basicity mold flux for high-Mn high-Al steels.