The buckling problem of cylindrical shells has been studied by many mechanic researchers from different points of view. In this paper, an elastic cylindrical hli with semi-infinite length is studied. Let its dynamic buckling under impact torque be reduced to a b$.trcation problem caused by propagation of the torsional stress wave. The btfurcation problem is converted to a solution of nonlinear equations, the lateral inertia effect on the dynamic buckling is also discussed. Finally, numerical computation is carried out, from this, some beneficial conclusions are obtained.