Abstract: The existence of cracks in cemented backfill roof is one of the main factors which influence the stability of roof.The determination of crack′s depth provides a precondition for the roof stability analysis.So ground penetration radar(GPR) technique is proposed to detect and indentify the cracks in cemented backfill.Firstly，the relative dielectric constant of cemented backfill was measured and the feasibility of crack detection using GPR was discussed.Then，based on the principle of radar and electromagnetic wave scattering and wave superposition at anomalies，it is obtained that the response characteristics of the radar wave is a hyperbolic wave group from the top to the end of vertical cracks，which was verified by the forward modeling.Lastly，detection on the roof cracks of cemented backfill for a copper mine was made，and the findings displayed as a hyperbolic wave group.The studies indicated that ground penetrating radar can be used to detect cracks in cemented backfill.

Key words: Cemented backfill, Ground penetrating radar(GPR) , Crack, Forward modeling, Field test