The work aims to improve the processing ability of the micro-abrasive water jet on hard and brittle materials, and improve the morphology and quality of the machined surface. Ultrasonic vibration was introduced to vibrate the workpiece vibrate at a small amplitude and given ultrasonic frequency perpendicularly to the target surface. The in-house developed ultrasonic-assisted micro-abrasive water jet processing device was used to carry out the micro-hole erosion processing experiment on the K9 glass, and the related experiments without ultrasonic vibration were also used to be as the comparisons. The 3D microscope was used to observe the micro-holes machined under various experimental conditions, in which the cross- sectional profiles of micro-holes were measured, and then the effect of ultrasonic vibration on the profiles and morphology of micro-holes were studied. It is found that the depth and top diameter of the micro-holes were positively correlated with the jet pressure and processing time. The introduction of ultrasonic vibration significantly increased the depth of the micro-holes, with the maximum increase in depth to about 54.6%, but the top diameter of micro-holes was slightly reduced, with the maximum decrease of 8.2%, and the overall material removal rate was increased. It is because that the ductile erosion dominated the material removal process, as a result, the cross section of the micro-holes was a typical “W” shape. However, with the ultrasonic vibration the “W”-shaped cross-sectional profile had been improved, where the material of the protruding part of the center of the micro- hole had been more removed, and the flatness of the bottom surface has been improved as well. Thus, the ultrasonic vibration, indeed, enhances the erosion performance of micro-abrasive water jet on K9 glass, the ultrasonic-assisted micro- abrasive water jet processing technology can realize high-quality and high-efficiency processing of hard and brittle materials such as K9 glass.