Air-coupled ground penetrating radar is widely used in areas with poor terrain conditions and many surface obstructions. In order to precisely evaluate the influence of surface obstructions on the air-coupled ground penetrating radar detection, the horizontal distance between surface obstructions and the detection object was quantitatively studied. The air-coupled ground penetrating radar principle was first used to design an indoor experiment. The influence of the distance between the obstacle and the detection object on the depth of detection and the amplitude changes of the reflection interface of the detection object was analyzed. The relevant laws were then verified by forward simulation. Finally, the relationship between the distance between the obstacle and the detection object and the parameters of the air-coupled ground penetrating radar when it was working was derived based on the analysis of the electromagnetic wave propagation laws of the air-coupled ground penetrating radar. The research results show that the physical experiment obstacles used for air-coupled ground-penetrating radar detection of underground objects have no significant impact on the detection depth. As the obstacle gradually moves away from the detection object, the amplitude of the reflection interface of the detection object will first increase and then stabilize. The amplitude increase stage follows an exponential function distribution law, and the amplitude stability stage has the same amplitude value as when there are no obstacles. In this paper, the distance between the obstacle and the target object at which the amplitude is just approaching stability is defined as the critical distance at which the obstacle affects the amplitude of the radar signal. The height of the antenna, the depth of the target object, the dielectric constant of the detection medium, and the angle of incidence of the electromagnetic wave are all related to the critical distance. The result quantifies the influence of surface obstacles on the physical characteristics of the air-coupled ground penetrating radar and provides guidance for the operation of air-coupled ground penetrating radar.