The methods for the interpretation of the thickness of the secondary lining, the distribution of the reinforcement bars and steel ribs and the compactness of the concrete are studied, so as to improve the accuracy of geological interpretation. The quality of the lining of Daquangou tunnel is detected by means of geological radar. The comparison and contrast between the detection results and the original design show that the geological detection is accurate and the interpretation method adopted in the geological detection is effective. Conclusions drawn are as follows: 1) Geological radar detection technology is simple, rapid and effective. 2) Geological interpretation can not be made until the signals obtained by the geological radar have been properly processed. 3) The detection of the second layer of reinforcement bar is affected by the antenna screening.