The aim of the study on the deformation defect is to prevent defects and to improve the quality and to control the deformation. It is important that the preventive measure could be established to advance the scientificity of the product and processing design. In this paper, the reasons of the outer defects such as cracks are analyzed based on the superplasticity of the copper alloy and the process of solid cages in the superplastic extrusion. The prediction and numerical simulation of these typical defects are also carried out using the Deform-3D software grounded on the model of the rigid-visco plastic FEM. The position, time of crack appearance and relation between the strain rate and the defects are also studied. The simulated results are in equivalent agreement with the experiment.