Abstract: In order to analyze the influence of obstracle in the opposite direction to radar deetction direction on data acquisition of ground radar, based on radar theory, using the finite difference method of time domain, the paper set up the corresponding geological model to conduct two-dimension forward modeling of ground penetrating radar. In combination with engineering cases, the data of radar detection in a tunnel in Fujian Province were analyzed and studied. The research results show that when a ground penetrating radar was used to detect a target object, electromagnetic wave did not emit nor propagate towards the detection direction, and electromagnetic waves would emit around the antenna, while the electromagnetic wave which was not at the detection direction would have some influence on the data acquired by the radar, disturbing the accuracy of data interpretation. Therefore, during utilization of the ground penetrating radar and interpretation of ground radar data, the site environemts must be known and the interference wave must be removed so as to achieve the correct judgement of the detected target object.