In order to acquire the law of acoustic propagation property of hard brittle shale formation, the shale of Shihezi formation in Ordos Basin are taken to be studied object, interval transit time, attenuation coefficient, time domain signal and frequency signal of hard brittle shale were sys-tematically analyzed before and after soaked on the drilling fluid used ultrasonic transmission experiment. The results showed that interval transit time and attenuation coefficient of shale in-crease, time domain signal and frequency signal change of shale after soaked on drilling fluid. Hydration occurs when shale is soaked on drilling fluid. interval transit time and attenuation co-efficient can quantificationally describe dynamically changes of hydration, time domain signal and frequency signal can qualitatively analyze changes of shale. ultrasonic transmission experiment offer a new idea for study the hydration characteristics of hard brittle shale.