The effect of hydrofluoric acid (HFA) on the upgrading and structure of oil shale from Yilan county, Heilongjiang province, China was investigated by the ultrasonic treatment of the shale in a mild water bath. The oil shale samples were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF) and scanning electron (SE) microscopies, as well as Fourier transform infrared (FTIR) spectroscopy, and densimetry. The results of the study indicate that the HFA-based ultrasonic treatment exhibited a better performance in upgrading oil shale than the ordinary mechanical stirring method. It was also found that the concentration of HFA significantly influenced upgrading performance and the separation degree of inorganic minerals. The kerogen content in oil shale increased with increasing concentration of HFA. The total content of C, H, O and N in oil shale reached 98.2% when 40% HFA was used. Oil shale is composed mainly of a chainlike cyclic saturated organic material called kerogen, and inorganic minerals such as quartz, kaolinite, illite, siderite and pyrite. These materials integrate into a smooth lithified sandwich by the hydrogen bond and intermolecular forces. Via the ultrasonic treatment under mild conditions, kaolinite and siderite can be removed from oil shale with the use of a weak HFA, while a stronger HFA is needed to leach illite and quartz. Then kerogen with a loose porous structure is obtained.