Abstract: The soundness diagnosis testing was carried out on the quality state of a tunnel at Fenghuo Mountain tunnel.This tunnel is one of the permafrost tunnels in frost soil area along the Qinghai-Tibet Railway line.The testing was done some years later after the railway was used. The tunnel is in alpine permafrost zone.The tunnel body is in the frozen rocks.At both ends of the tunnel,the dominant rocks are sandstone and shale,where the frozen soils are ice-rich.Due to the seasonal effects of freezing and thawing,defects were appear in the tunnel more and more. The defects are manifested mainly as lining cracks,leaking and gushing water,lining crisp peeling.In order to accurately understand the quality state of the tunnel lining,the geological penetrating radar technique was used to defect and quantify the defects in the tunnel field.The technique was applied to the tunnel lining structure quality inspection.The technique changed the traditional destructive testing method.The technique is fast,simple,non-destructive,and accurate.Through the in-situ data processing and analysis,the technique can accurately detect lining thickness,find out of lining and filling the empty space behind the non-dense area.The test results show the following.The tunnel in the frozen atrocious weather environment,the lining appearance was not damaged.Seepage was found in the openings of two ends.The lining with empty is the most serious defect level and had a measured length of 20m.The line with the secondary serious defect level had a length of 98m.The lining backfill behind the non-compact class is the third serious defect level and has a measured length of 41m.The most serious level has a line length of 33m.Test results are basically consistent with the actual defect situation. The results can provide a scientific basis for normal operation of the tunnel and reliable foundation for defect treatment in the future.Practical evidence proved the use of geological penetrating radar to make health diagnostic tests for the tunnel is feasible.