Abstract: Geological conditions of subway foundation pit bottom should be taken care of to guarantee the safety of construction and operation of subway in karst area.It has shown that geology method should be given the first place together with other auxiliary methods considering the features of subway construction.This paper described principle,technology character of GPR and practical working Method and using an application of the successful detection of the karst in a foundation pit of Wuhan metro Line 2 as example, confirms the effectiveness and feasibility of the method in the exploration of hidden karst in foundation pit.The technique is worthy of wide application with further improvement.