The physical and mechanical properties of wet-milling ultra-fine grouting cement were studied,and its microstructure was observed through modern instrumentation analysis such as scanning electronic microscopy(SEM),X-ray diffraction and Hg-intrusion micromeritics.The experimental results indicate that wet-milling ultra-fine cement possesses high rheological properties and groutability.It can be filled densely in cracks of rock and hydrate fully,which may endow hydrated cement with high mechanical strength.Main hydration products of wet-milling ultra-fine cement are poorly crystalline C-S-H(Ⅰ),acicular AFt and plank-shape Ca(OH)2.The dense crystal-network structure can be formed in the rock gaps filled with cement paste,but some weak regions exist owing to Ca(OH)2.The features of micro-pore structure of hydrated wet-milling ultra-fine cement are few big harmful pores,abundant harmless micro pores and little most possible pore radius.