Abstract: The computerized tomographic scanner (CTS) was used to investigate the dynamic weakening process of the mudrock meso-structure when interacting with water. A series of real-time scanning tests were performed on the mudrock specimen soaked for different time. The space-time evolution characteristics of water-induced cracks inside mudrock， including the original fracturing effect， netty extension behavior， spatial nonuniformity distribution and active period of reaction， were exposed dynamically by CTS. The water-weakening process of the mudrock meso-structure can be divided into the following steps: firstly， inherent micro fractures provide the initial path for water to invade into unloaded mudrock; then the incursive water induces the volume increase of clay minerals and ion solution of carbonate through physical and chemical reactions; finally， the adverse mechanical impact derived from the volume expansion and solution of carbonate leads to the propagation and connection of cracks.

Key words: engineering geology, mudrock, water-weakening process, CT observation, mechanism