The detection of hidden dangers in Jinjiang reservoir dam with ground penetrating radar shows that themajor hidden dangers of the dam are the karst caves in the dam basement rocks and the soil caves which were formedin the residual sola and talus sofa by percolating channels such is faults and fissures. Another hidden danger is theweakening of the impervious ability of the dam resulting from the closeness of the height of line seepage of the reservoir water level to the contact plane between the residual solum, talus solum and basement rocks. Meanwhile, as thedepth of grouting and the diffusion radius of the cement in grouting project can be shown by Ground PenetratingRadar images, this technique can become a new non-destructive test technology in dyke and dam grouting projects ofthe water conservancy department.