Compressive tests after low velocity impact were carried out on Nomex honeycomb core sandwich specimens. Some methods were used to study the cause of damage development when the specimens were compressed to fail: X ray, deply, and visual inspection. Compressive failure mechanism was analyzed. The results showed that the residual compressive strength decreased while impact energy increased. The compressive failure of Nomex honeycomb core sandwich specimen was controlled by the front facesheet.The loads that caused the front facesheets to buckle was close to the load that made the planes fail. The glass cloth on surface not only could reduce impact damage, but also could show the damage within the plane on the surface so that it could been found easily.