The present paper is to analyses the key parameters of multi-reflection in GPR Survey. At first, it introduced the theory and methods for GPR result explanation. Then it proposed the necessity to work on multi-reflection analysis. For the complexity of multi-reflection, it emphatically worked on secondary reflection. According to the distinction of travel routes, the secondary reflection was divided into two cases. In the first case, the incident wave reflected twice at every interface and in the second case, the incident wave reflected for twice at every layer, meanwhile, the second reflected wave penetrated into the next layer as new incident wave. In these two cases, the amount of received waves was different and their corresponding transmitting parameters were deduced in the present paper. According to the deduction, in the situation of multiple reflections, the two-way travel time increases gradually; the energy decreases sharply and the profile curves are similar to each other.