The authors have analysed the present situation of the α-measuring Rn method and its application,and developed the α-cup Rn measuring technique by experimental study in the light of existing problems.The principle,the function,the working method and the application of α-cup measuring Rn are discussed in detail in this paper.The results show that the α-cup method is characterized by high sensitivity,simple operation,high efficiency and low cost and hence can be used to find the bedrock groundwater,probe into hidden geological structure,and solve engineering geological problems.Being a new nuclear geophysical method,it deserves to be spread in the field of application.