Abstract: Polytetrafluoroethylene(PTFE) inserts are usually used as artificial disbond defects when making reference samples containing disbonds in the insulator of solid rocket motors. It is hard to take out the inserts in most cases. There will be air gaps once the poor bonding between the insert and the host material appears, in addition, the upper surface of the sample will bulge. In this paper, first, it is proven that the PTFE insert leads to a hybrid defect which consists of the insert and air gaps; then a variety of models are established for the different composition, position and bulge of the defect, and the corresponding numerical simulation is conducted; at last, a precise and simple modeling method is presented by comparing and analyzing the simulation results of these models.