Abstract: The main exploitable ore body in the Xinli mine area occurs in an undersea rock mass. In order to ensure the safety of undersea mining, it is of great significance to verify the seepage characteristic of the rock mass in the Xinli mining area. The calculation process of permeability coefficient tensor and synthetic permeability coefficient of the fractured rock mass were introduced in detail. The calculation program of permeability coefficient tensor was developed with the Visual C#. The conditions of hydrogeology and engineering geology of the Xinli mining area were analyzed. Based on the fractures geometry data surveyed in situ, the permeability coefficient tensors of the rock mass at levels of -105, -135 and -165 m above the sea level were calculated. The results were modified in terms of downhole permeability tests. The modified results indicate that the rock mass has weak permeability at levels of -105 and -135 m above the sea level on the whole and micro-weak permeability at level of -165 m above the sea level. The permeability reduces with the buried depth of the rock mass.