In order to study the kinematics and mechanism of the fold and thrust belts, writers designed and finished three types of sandbox experiments. Each model included two detachments in different depths. And writers calculated the displacement fields in the model sections in the processes of the experiments using particle image velocimetry (PIV) technique, to get a better understanding of the kinematics. The results indicate that the deep detachment dominated the structure and evolution of the fold and thrust belt, and locally shallow structure was controlled by the upper detachment. This conclusion was demonstrated by comparing the modeling results with the natural example in the south segment of the fold and thrust belt in Longmen Mountains. PIV analysis suggests that， in the primary stage, deformation was characterized by parallel shortening of the sand layers. Deformation above and below the ductile layer is quite different. Deformation upon the ductile layer propagated faster and farther. After more horizontal compression, thrust began to generate and the rupture would happen. Once the fault initiated, the velocity in the foot wall decreased to zero, and deformation was localized on the fault plane, the hanging wall thrusted up synchronously.