Study of metal flow in extrusion billet is fundamental and useful to understand extrusion technology. Investigation of behavior of extrusion billet skin and microstructure of products is indispensable to maintain qualities of extrusions. In order to research the behavior, experiments and FE analysis of clad billet extrusion were performed. The analytical results of billet skin deformation were similar to that in experiments. Friction between back end of billet and ram affects the deformation of skin and its penetration into billet. Secondly, microstructure of an extruded product is predicted and the condition of recrystallization and grain refnement is revealed.