Abstract: An experimental model with two cavities was made of concrete, ore fines and tails in the laboratory. Simulation experiments were conducted to study the characters in Ground Penetrating Radar (GPR) images of every filling body by filling water, sand, mud and air in turn. Experimental results indicate the radar image changes with gob filling. Field investigations were carried out at Changba Lead-zinc Mine in China. The main detecting method for gob and its filling by GPR was expounded. The space distribution of gob was obtained. The filling can be well identified by analyzing the radar images. The results of field experiments show GPR technique is useful, high-efficiency and nondestructive for detecting gob and its filling.