SPH (Smoothed Particle Hydrodynamics) method is applied to impact crush/buckling problem of circular tube. It has been known that there are several kinds of buckling modes by axial impact load. First, elastic analyses of the crush/buckling are conducted, and three types of typical crush/buckling shape are obtained. Following the elastic analyses, elastic-plastic analyses were performed to improve the accuracy of the simulation. The shape of the buckling and the energy absorbed by circular tube are discussed.