The highway reconstruction and expansion project is in a period of rapid development in Guangdong Province. How to accurately obtain the condition of the road surface disease is the main problem faced by the formulation of the old road treatment plan. Relying on the Kaiyang Expressway reconstruction and expansion project, the three-dimensional ground penetrating radar was used to detect the disease on the old road, and the disease distribution on the surface and inside of the road was obtained, and the road conditions were compared with the actual conditions after the manual walk and the excavation. The results show that when the 3D ground penetrating radar detection sampling interval is set to 2.0cm, the standing wave time is set to 0.6ms, and the time window is set to 85ns, better detection accuracy can be achieved; Detect cracks at different depths, accurately identify 3mm wide cracks, and direct the development direction and nature of the cracks.