The relationship between determining lower limit of groundwater activities and sitting permanent deposing nuclear waste material is discussed in this article. These views are based on tho experience of teaching and scientific research and analysing hydrogeological features of exploration site in Long Men Mountains, which includes following coateutsi (1) Lower limit of groundwater activities involved in groundwater formation, (2) Different features of lower limit of groan-water activities in different hydrogeological conditioasi; (3) Change of lower limit of groundwater actirities; (4)Determination of lower limit of groundwater activities; (5) Discussing the lower limit of groundwater activties of exploration site in Long Men Mountains; (6)The hydrogeo logic principles of sitting permanent deposing nuclear waste material.